Open Journal of Modern Linguistics
2012. Vol.2, No.3, 114-124
Published Online September 2012 in SciRes (http://www.SciRP.org/journal/ojml) http://dx.doi.org/10.4236/ojml.2012.23015
114
Taking the Guesswork Out of Curriculum Design:
Learning to Engineer Explicit Grammar Curricula through the
Analysis of Multiple Influences on the Acquisition Process
Andrew D. Schenck, Wonkyung Choi*
Department of Liberal Arts Education (LAEC), Ju Si-Gyeong College,
Pai Chai University, Daejeon, *South Korea
Received June 21st, 2012; revised July 21st, 2012; accepted July 28th, 2012
While a study by Goldschneider and DeKeyser (2005) was able to explain how factors such as phono-
logical salience, frequency, morphological regularity, semantic complexity, and syntactic complexity in-
fluence acquisition order, the examination of six similar morphological features provided only a limited
perspective. The purpose of this study was to see if causal variables, both individually and cumulatively,
could be used to predict acquisition orders with more highly disparate morphological and syntactic fea-
tures. Results of Spearman rank calculations revealed that the integration of causal factors yielded the
highest correlation to both the Processability Theory (rs = 0.821; p = 0.007) and Natural Order Hypothesis
(rs = 0.529; p = 0.143), suggesting that these factors have a synergistic influence on morphosyntactic de-
velopment. Methods to predict the acquisition of both syntactic and morphological features are suggested,
along with an empirically-based method to guide explicit grammar instruction.
Keywords: Explicit Grammar Instruction; Processability Theory; Natural Order Hypothesis; Acquisition
Order; Frequency; Morphosyntactic Complexity
Introduction
Although explicit grammar instruction has been extensively
investigated (Norris & Ortega, 2000; Spada & Tomita, 2010), a
debate concerning its efficacy persists today. Some researchers
argue that the effects of this instruction are ephemeral and of
limited use in production tasks (Tode, 2007; Truscott & Hsu,
2008), while others purport that it can bring about significant
improvement (Ellis, Sheen, Murakami, & Takashima, 2008;
Norris & Ortega, 2000; Spada & Tomita, 2010).
In reality, the debate concerning explicit grammar instruction
is being fueled by a deficiency in theoretical understanding of
the second language acquisition process. Although several his-
torical studies document a clear sequence of acquisition for L2
learners (Cook, 2001; De Villiers & De Villiers, 1973; Dulay &
Burt, 1974; Dulay, Burt, & Krashen, 1982; Krashen & Terrell,
1983; Pienemann, 1999, 2005; Simmons, 2001), they have failed
to provide a holistic perspective from which effective explicit
grammar curricula can be created. Three main methodological
flaws have prevented the development of a holistic perspective
that can be applied to practice.
First, historical studies have not examined acquisition orders
large enough to effectively guide the sequencing of explicit
grammar lessons. Rather than extending the limited order of 14
morphemes first discovered by Brown (1973) in the 1970s, suc-
cessive studies continued to examine only a few morphosyntac-
tic features in isolation, numbering from 10 to 14 (De Villiers
& De Villiers, 1973; Dulay & Burt, 1974, 1975; Krashen & Ter-
rell, 1983; Johnston, 1985, 1994; Pienemann, 1999, 2005). These
designs have had only limited utility, because they illuminate
only a small facet of a more complex acquisition process. In
addition, each research project used different participants at
disparate developmental levels, meaning that results, which
contained different morphosyntactic features, could not be
cross-referenced to provide a more holistic perspective.
Secondly, morphosyntactic features have not been catego-
rized in an organized way, obfuscating results that could be
used to improve instruction (Cook, 1993). A study by Dulay
and Burt (1975), for example, separately examined two allo-
morphs for the plural morpheme (-s/-es) while allomorphs for
both the copula and progressive auxiliary (’s/is) were placed
within a single category. Other research studies, in contrast,
included the plural -s and long plural -es within one category
and separated the contractible copula and auxiliary features
from non-contracted forms (Dulay, Burt, & Krashen, 1982).
Because researchers have not categorized morphosyntactic
features consistently, educators have had difficulty determining
how these features should be integrated within one curriculum.
Finally, historical acquisition order research has not accu-
rately defined causes of the sequence of acquisition, inhibiting
the ability of educators and curriculum designers to predict how
modification of explicit grammar curricula will affect perform-
ance. Cook (1993) commented that:
The order of acquisition is not the reason behind errors; it
is a generalisation about errors which still lacks a reason.
To me, such remarks are more like Newton announcing
that apples fall to the ground than the discovery of the the-
ory of gravity—describing one limited instance rather
than explaining it (p. 44).
*Corresponding author. Just as this statement implies, the lack of an explanation for

A. D. SCHENCK, W. CHOI
acquisition order has severely limited the significance of the
findings. SLA researchers must understand why the phenome-
non occurs, since manipulation of a cause is a necessary pre-
cursor to the engineering of a desired effect. To date, attempts
to adapt acquisition order to practice have focused on the ac-
quisition order phenomenon itself, rather than its underlying
causes. In the 1980s, for example, Pienemann (1995, 1999) at-
tempted to explain what morphosyntactic features were “teach-
able”, based upon the developmental level of the ESL learner.
Later, Hill and Flynn (2008) also developed a set of questions
that were designed to elicit language found at different SLA
stages, from the Preproduction Stage to the Advanced Stage.
Ultimately, for acquisition order to be useful in practice, edu-
cators must know both the causes of the phenomenon, and the
means to manipulate these causes to obtain a desired result.
Due to the limited size of acquisition orders, inconsistencies
with the classification of grammatical features, and undefined
causes of the acquisition process, past research of morphosyn-
tactic development has been of limited use to educators and
curriculum designers. Such problems have precluded the ability
of educators to accurately predict how changes to explicit
grammar curricula will influence the acquisition process. As a
consequence, educators are now forced to rely on intuition
when designing explicit grammar curricula, which explains
why such curricula do not appear to parallel known research of
morphosyntactic development (Biber & Reppen, 2002).
Literature Review
Brown (1973) was one of the first researchers to examine the
similarities of morphosyntactic development among different
language learners. In the 1970s, he discovered an “invariant”
order of acquisition for children learning English as their L1.
Following this discovery, researchers such as Dulay and Burt
(1974, 1975) also discovered that children learning English as a
second language acquire morphosyntactic features in a distinct
order. Krashen and Terrell (1983), through the synthesis of past
ESL studies, developed a 4 stage hierarchy of morphosyntactic
development termed the Natural Order (Table 1). According to
this order, progressive, copula, and plural morphemes were ac-
quired in early stages, while past tenses, the third person singu-
lar, and possessive morphemes were acquired late in the acqui-
sition process.
The Processability Theory
Following the discovery of morphological sequences of ac-
quisition, both Johnston (1985, 1994) and Pienemann (1999,
2005) discovered a sequential list of morphosyntactic develop-
ment referred to as the Processability Model. Like prior re-
search of morphological sequences, grammatical elements of
this model appeared to be universal, regardless of factors such
as age or linguistic background (Pienemann, 1999, 2005; Cook,
2001). Unlike prior research of morphological features, how-
ever, the Processability Model included several syntactic fea-
tures involved in the construction of questions and complex
clauses.
Grammatical features were organized into six discreet stages,
which revealed the development of speech from small phrases to
complex sentences (Table 2). The first two stages describe the
development of basic SVO syntax and individual phrases. In
stage two, learners begin to organize words into SVO sentences
Table 1.
Stages of the natural order.
Stage Natural Order Hypothesis
Krashen & Terrell (1983)
1
Progressive (-ing)
Plural (-s)
Copula (is)
2 Singular Auxiliary (is)
Article (a, the)
3 Past Irregular
4
Regular Past
Third Person Singular (-s)
Possessive (-s)
Table 2.
Stages of the processability model.
Stage Processability Model
Pienemann (1999) & Johnston (1985)
1 Single Words
2 SVO Sentences
Plural (-s)
3
Negative + Verb
Do-Fronting
Topicalization
Adverb-Fronting
4
Yes/No Question Inversion
Particle Verb Separation
Wh-copula Question Inversion
5 Wh-auxiliary Question Inversion
Third Person Singular (-s)
6 Cancel Inversion
and use morphosyntactic features (e.g., plural -s) to build more
complex phrases (Mitchell & Myles, 2004).
Stage three is marked by the use of adverbials, do-fronting,
topicalization, and negation. During this stage, grammatical
features are simply moved to the front of a phrase or sentence.
The do auxiliary verb, for example, is moved to the front of the
sentence to form a question, as in the example, Do you like it?
This movement, referred as do-fronting, is posited to occur
without any conjugation of the auxiliary do verb. Topical noun
phrases are also moved to the head of a sentence in a process
called topicalization. Learners begin to use sentences such as
That, I like. Finally, sentences are negated by putting the word
no in front of a verb phrase. The sentence I no like that is an
illustration of this process (Pienemann, 1999, 2005).
At stage four, morphological development requires manipu-
lation of multiple phrases (Pienemann, 1999). Learners begin to
change phrasal elements within a sentence, through inverting
the subject and verb in yes/no (e.g., Has he read the book?) and
copula (e.g., What is he doing?) questions. Students also ma-
nipulate phrases by embedding an accusative nominal phrase
within a separable particle verb, as in the following example, I
put the book in the bookcase (Cook, 2001). During stage five,
learners continue to master use of multiple phrases through the
inversion of auxiliary verbs within Wh-questions and inflection
of the third-person singular morpheme (Pienemann, 1999, 2005).
During stage six, learners begin to use larger subordinate
clauses to change elements on a sentential level. They use can-
cel inversion, which refers to the absence of inversion found in

A. D. SCHENCK, W. CHOI
the subordinate clause of an embedded question (e.g., Could
you tell me where the bank is?). This represents the final stage
of the Processability Model (Cook, 2001; Pienemann, 2005).
Unlike previous models, which included only morphological
features, the Processability Model included more complex syn-
tactic features that modify phrases (question inversion) and
larger clauses (cancel inversion). Recently, even more complex
connectives (e.g., but, and, then, when, because), which modify
elements on a sentential level, have been found to emerge in a
distinct order (Evers-Vermeul & Sanders, 2009).
Causes of Acquisition Order
Although each morphosyntactic sequence was insightful, re-
searchers could not agree about causes of the phenomenon,
which limited the degree to which it could be utilized or engi-
neered to improve instruction (Cook, 1993). In the early 1970s,
when research of morphological sequences first began, Brown
(1973) proposed several causes for the acquisition phenomenon,
namely, semantic complexity, syntactic complexity, and input
frequency. This sparked a debate over the validity of each indi-
vidual factor, which served to obfuscate the interrelated nature
of the multiple causes. While De Villiers and De Villiers (1973)
agreed that syntax and semantic causes could explain the acqui-
sition process, they concluded that frequency had no apparent
role. Larsen-Freeman (1976), in contrast, posited that a signify-
cant correlation existed between acquisition order and fre-
quency. Dulay and Burt (1974) downplayed the role of seman-
tics, citing that L2 learners already possessed a complex se-
mantic understanding through their L1, and, therefore, were not
impeded by this factor. They, instead, explained acquisition as a
product of the interaction between innate systems governing the
development of syntax and the surrounding input.
In the 1980s, researchers such as Pienemann (1999, 2005)
and Johnston (1985, 1994) posited that syntactic complexity
determined the emergence of morphosyntactic features. First,
learners use single words and lexical morphemes (e.g., the plu-
ral -s) that require no exchange of grammatical information. At
higher stages of development, learners use grammatical features
that require an exchange of information between phrases (e.g.,
third person singular) and clauses (e.g., cancel inversion) (Pie-
nemann, 2005). As in previous studies of morphosyntactic ac-
quisition, this theory is not consistently accurate. Recent re-
search reveals, for example, that the model does not accurately
predict the order of acquisition for each morphosyntactic fea-
ture with equal certainty (Dyson, 2009; Lee, 2006). While the
model tends to correctly predict the sequence of syntactic fea-
tures, it often fails to accurately predict when morphological
features will be mastered (Dyson, 2009).
Following the exploration of causes such as syntax, seman-
tics, and frequency, researchers began to realize that phono-
logical characteristics of grammatical features also influence
the acquisition process (Ellis, 2002). In the 1990s, research re-
vealed that aspects of phonology influence the processing and
interpretation of linguistic features (Saffran, Aslin, & Newport,
1996). A follow-up study also revealed that young learners are
sensitive to syllable sequences, further suggesting that phono-
logical characteristics of a grammatical feature may influence
its interpretation and use (Pelucchi, Hay, & Saffran, 2009). To
date, there is a large research corpus which confirms the exis-
tence of a strong link between phonology and morphosyntactic
development (Martohardjono, 1989; McCarthy, 2004; Gass &
Selinker, 2008).
In the early 21st century, new research emerged which inte-
grated and analyzed known causes of the acquisition process to
provide a more holistic perspective (Evers-Vermeul & Sanders,
2009; Goldschneider & DeKeyser, 2005; Rowland, Pine, Lie-
ven, & Theakston, 2003). Although such research studies par-
tially explained the order of acquisition through collective ana-
lysis of phonological salience, frequency, morphological regu-
larity, semantic complexity, and syntactic complexity, the lim-
ited coverage of grammatical features in each study was of little
utility to educators (Evers-Vermeul & Sanders, 2009; Gold-
schneider & DeKeyser, 2005; Rowland, Pine, Lieven, & Theaks-
ton, 2003). A study by Goldschneider and DeKeyser (2005), for
example, was limited to only 6 morphological features (present
progressive -ing; plural -s, possessive -s; articles a, an, the; 3rd
person singular -s; and regular past -ed). Three of the six fea-
tures investigated were homophonic, bound morphemes (plural
-s, possessive -s; 3rd person singular -s), meaning that values for
characteristics such as phonological salience, morphological
regularity, and syntactic complexity were equal. Lexically ac-
quired features and aspects of syntax (e.g., past irregular tense
and question inversion), which have a large number of variants
and a high degree of phonological salience, were not examined.
Although modern studies continue to investigate causal fac-
tors of acquisition, they largely avoid the search for universal
grammatical relationships, in favor of designs which examine
individual morphosyntactic features and their causes (Boss,
2008; Bettoni & DiBiase, 2011; Chang, Kobayashi, & Amano,
2009; Friedmann & Costa, 2011; Maguire et al., 2010; Wester-
gaard, 2009; Williams, 2010). As with prior studies of mor-
phosyntactic acquisition, these studies do not facilitate devel-
opment of a holistic perspective which is needed to guide the
design of explicit grammar curricula. To address this limitation
within past research, the current study was designed to examine
a large number of highly disparate morphosyntactic features,
such as those included in the Processability Theory and Natural
Order Hypothesis.
Research Problem
Although some research studies have partially explained the
order of acquisition through collective analysis of phonological
salience, frequency, morphological regularity, semantic com-
plexity, and syntactic complexity, the limited coverage of gram-
matical features is of little utility to educators (Evers-Vermeul
& Sanders, 2009; Goldschneider & DeKeyser, 2005; Rowland,
Pine, Lieven, & Theakston, 2003). To expand the utility of
former research and provide a guide for explicit grammar cur-
ricula, analysis of more highly disparate morphological and
syntactic features contained in the Natural Order and Proc-
essability Model were analyzed. The following questions were
posed:
1) Can values of phonological salience, frequency, morpho-
logical regularity, semantic complexity, and syntactic complex-
ity for each morphosyntactic feature be used to predict orders of
the Processability Theory and Natural Order Hypothesis (Kra-
shen & Terrell, 1983; Pienemann, 2005)?
2) Does the integration of causal variables (phonological sa-
lience, frequency, morphological regularity, semantic complex-
ity, and syntactic complexity) for each morphosyntactic feature
more accurately predict orders of the Processability Theory and
Natural Order Hypothesis than consideration of individual causes
116

A. D. SCHENCK, W. CHOI
alone (Krashen & Terrell, 1983; Pienemann, 2005)?
Predictions of the acquisition process will help researchers
and educators further understand how multiple causes influence
morphosyntactic development. This understanding, subsequently,
may be used to engineer curricula to hasten the acquisition
process.
Method
To address research question one, which attempted to ascer-
tain if individual causes had predictive validity, the nonpara-
metric Spearman rank correlation formula was used to correlate
values of phonological salience, frequency, morphological re-
gularity, semantic complexity, and syntactic complexity to the
rank orders of features contained within the Processability
Model and Natural Order.
To address research question two, which attempted to ascer-
tain if the integration of causes had a higher predictive validity,
all causal variables were combined into one predicted acquisi-
tion order through four steps. First, values for semantic com-
plexity, morphological alternations, and morphosyntactic com-
plexity were made negative, since larger values may slow the
acquisition process, while values for sonority and frequency,
which may hasten acquisition when values are higher, remained
positive. Second, all scores for phonological salience (sonority),
morphological regularity (alternations), frequency, semantic com-
plexity, and syntactic complexity were converted to z scores.
Third, these z scores were averaged together to get one overall
score for each morphosyntactic feature. Finally, the overall
scores were ordered from the highest to the lowest value to
construct the hypothesized acquisition order.
After the predicted acquisition order was calculated, it was
correlated to the Natural Order and Processability Theories
using the Spearman rank correlation formula. As in the correla-
tion of individual causal factors, the limited number of features
(16) and the predominance of ordinal data made this statistical
formula the best choice.
Operational Definition of Variables
Frequency
Frequency refers to the number of times a morphosyntactic
feature is present within input (Goldschneider & DeKeyser,
2005). This ratio scale variable was obtained by using the Cor-
pus of Contempora ry American English (COCA) (Davies, 2008).
This corpus, which contains 425 million words obtained from
various sources of discourse in an American context, provided
the means to search most morphosyntactic features contained
within both the Processability Model and the Natural Order
(See Appendix A for a list of corpus search strings and fre-
quency values). In some cases, multiple search strings were
needed for one grammar type. For Wh-questions, for example,
single-word interrogative pronouns such as where or when had
to be searched separately from those using two-word interroga-
tive pronouns such as how long and how far. After multiple
searches were executed, values were added to arrive at a total
for the morphosyntactic feature.
Due to limitations of the corpus search engine, values for single
words, SVO sentences, topicalization, and adverb-fronting could not
be obtained. Since all of the components in search strings for these
features appeared in the Corpus more than 10,000,000 times, the
corpus search engine would not execute the searches. These
features, therefore, had to be excluded from the investigation.
Determining frequency for negation from the Processability
Model was difficult because it is an interlanguage feature. Pie-
nemann (2005) defines negation as “an interlanguage form of
negation where a lexically invariable form of a negator is used
in preverbal position” (p. 19). According to this definition, in-
variable negation words no and not were included in the search
to obtain a value for frequency.
Morphosyntactic Alternation
Morphosyntactic alternation is a ratio scale variable that re-
fers to the number of different forms a grammatical feature may
take. For morphological features, it was assessed by calculating
the number of allomorphs. The plural -s morpheme, for exam-
ple, which has three allomorphs, s, z, and ɪz (used with nouns
such as books, pens, and cages, respectively), was assigned a
variability value of 3. While this method of calculation mir-
rored that used within the study by Goldschneider and Deyser
(2005), some modifications were made to increase accucy. The
indefinite articles, a and an, for example, were exnded from
two (e and æn) to four allomorphs (e and æn; ə and ən) because
of the common use of both phonological variants within every-
day speech. To estimate the total number of altertions for
highly variable features such as the past irregular tense and
separable phrasal verb, lists of these features from a comn Eng-
lish textbook were tallied (Master, 1996).
Variability for syntactic features was calculated by separate-
ing the words within each syntactic feature into discreet catego-
ries and multiplying the total number of variants in each cate-
gory to get a final estimate of alternations. Wh-auxiliary ques-
tions, such as those defined by Pienemann (1999), for example,
were separated into three categories: interrogative, auxiliary
verb, and subject pronoun (See Table B1 in Appendix B). Al-
though subject pronouns cannot account for all subjects that
may be used within questions, research of the Corpus of Con-
temporary American English (COCA) indicates that such pro-
nouns account for more than 90% of the subjects used within
question inversion and, thus, have been used to represent the
subject category (Davies, 2008). The word lists for each cate-
gory were obtained from Systems in English Grammar by Mas-
ter (1996). The total number of variants in each category was
then multiplied to estimate the total number of forms that could
occur. Morphosyntactic variation for Wh-auxiliary questions,
for example, was calculated by multiplying the number of inter-
rogatives (11) by the number of auxiliary verbs (18) and the
number of subject pronouns (7) for a total of 1386 alternations.
Do-fronting, which requires one non-conjugated do verb, was
calculated by multiplying 1 (Auxiliary do) by 7 (Subject pro-
nouns), for a total number of 7 alternations.
Phonological Salience
Phonological salience refers to the ease with which a mor-
phosyntactic feature can be heard (Goldschneider & DeKeyser,
2005). This ratio scale variable was calculated by determining
only the feature’s sonority, which is the degree to which the
vocal tract is open during articulation (Yavas, 2010). For this
study, two scales by Laver (1994) and Hogg and McCully
(1987) were integrated to provide the most comprehensive scale
for analysis (See Table B2 in Appendix B). The sonority value
for each morphosyntactic feature was calculated in two steps.
First, the phones (distinct units of sound) of each variant of a

A. D. SCHENCK, W. CHOI
118
morphosyntactic feature were added using the sonority scale.
Second, the resulting values for each variant were added, and
then divided by the total number of variants to get an average
sonority value. The resulting value was used to represent the
phonological salience of the target feature.
Although the number of phones and syllabicity were also in-
cluded in the calculation of phonological salience by Gold-
schneider and DeKeyser (2005), only the sonority value was
used within this study. This is because the number of phones
and syllabicity are both reflected in the calculation of the so-
nority value. Morphemes with a larger number syllables, for
example, have a higher sonority score (the vocal tract is open
more when vowels of a syllable are produced).
Semantic Complexity
Semantic complexity is a ratio scale variable that refers to the
total number of meanings conveyed by a morphosyntactic fea-
ture (Goldschneider & DeKeyser, 2005). To calculate semantic
complexity, the number of meanings conveyed by each gram-
matical structure were added using the method devised by
Brown (1973) (See Table C1 in Appendix C). New meanings
were also assigned to morphosyntactic features not described
by Brown. Interrogatives, for example, were assigned the se-
mantic designation question. In addition to earlierness, future
was added to cover any features that have a future meaning.
Finally, attributes were added to articles to better explain their
semantic complexity. As pointed out by Goldschneider and De-
Keyser (2005), the nonspecific attribute is far too simplistic to
explain article use in its entirety. Therefore, in addition to the
specific-nonspecific attribute, the distinction between common
and proper nouns, mass and count nouns, and use for generic
statements were included, for a total semantic complexity value
of four.
Morphosyntactic Comple xity
Morphosyntactic complexity refers to the degree of difficulty
learners have acquiring a new grammatical feature. To rate each
feature, a categorization system based upon an ordinal scale
ranging from 1 (the least complex) to 6 (the most complex) was
devised. The scale is based on the Processability Model, which
suggests that less complex intra-phrasal aspects of morphology
are acquired first, followed by more complex inter-phrasal and
inter-sentential aspects of syntax (Pienemann, 1999). As in the
study by Goldschneider and DeKeyser (2005), intraphrasal mor-
phological features were further divided into lexical/functional
categories, which were then subdivided into the free/bound
categories (Zobl & Liceras, 1994). Syntactic features, which re-
ceived higher scores, were divided into inter-phrasal and in-
ter-sentential categories to account for the complexity of infor-
mation exchange between constituents such as phrases (e.g., par-
ticle separation and question inversion) or clauses (e.g., cancel
inversion) (Pienemann, 1999). According to Table C2 in Ap-
pendix C, free lexical morphemes are hypothesized to be ac-
quired first, while inter-phrasal features are thought to be ac-
quired last.
Results
Correlations of individual causes (frequency, sonority, com-
plexity, morphological alternations, and syntactic complexity)
revealed several notable results (See Table 3).
Frequency was the only factor which was positively corre-
lated, albeit insignificantly, to the Processability Model (rs =
0.547). The positive correlation may reflect the factor’s ten-
dency to hasten the acquisition process as its value increases. In
contrast to frequency, all other causal factors had negative cor-
relations. Both morphosyntactic complexity (rs = –0.797) and
morphosyntactic alternations (rs = –0.673) were highly signify-
cant to the 0.05 probability level, suggesting that these two fac-
tors are influential in slowing the acquisition of features in the
Processability Model. The negative value of semantic complex-
ity (rs = –0.650; p = 0.058), which was nearly significant to the
0.05 probability level, may also have a role in slowing the ac-
quisition process. While negative correlation values for com-
plexity and alternations can be understood without difficulty,
the negative correlation for sonority cannot easily be explained.
In contrast to the correlations of the Processability Model,
individual causes did not correlate highly to the Natural Order.
The highest correlations, sonority (rs = 0.456) and frequency (rs =
0.477), were both positively correlated to the Natural Order,
suggesting that these causes may accelerate the acquisition
process as their values increase. Semantic complexity’s small
correlation value (rs = 0.107) suggests it has a weak, if any, link
to the acquisition process.
After causal variables were integrated, an acquisition order
was constructed (See Appendix D) and correlated to the Proc-
essability Model and the Natural Order. While individual causal
variables partially correlated to features found in the Proc-
essability Model and Natural Order, the collective integration
of factors into one predicted acquisition order yielded even
stronger correlations (See Table 4).
Correlation of the predicted acquisition order to the Proces-
sability Model, rs = 0.821, was significant to the .01 probability
level. This correlation was higher than any of the individual
causes alone, suggesting that causal variables have a synergistic
Table 3.
Correlations to the processability model and natural order.
Semantic ComplexitySonority
Morpho-Syntactic
Complexity Frequency Morpho-Syntactic Alternations
Processability Model rs –0.654 –0.612 –0.797a 0.547 –0.673a
p 0.056 0.080 0.010 0.127 0.047
N 9 9 9 9 9
Natural Order rs 0.107 0.456 –0.268 0.477 –0.005
p 0.785 0.218 0.485 0.195 0.991
N 9 9 9 9 9

A. D. SCHENCK, W. CHOI
Table 4.
Correlations to the processability model and natural order.
Predicted Sequence of
Acquisition
Processability Model rs 0.821a
p 0.007
N 9
Natural Order rs 0.511
p 0.160
N 9
influence on the acquisition process. Correlation to the Natural
Order (rs = 0.511; p = 0.160), likewise, was higher than indi-
vidual causal correlations, supporting the claim that individual
causal variables are partial determinants of acquisition order.
Overall, the predicted sequence of acquisition was able to
explain acquisition of features in the Processability Model much
more effectively than those in the Natural Order. Analysis of
the predicted acquisition order in Appendix D reveals that syn-
tactic features, which are only represented in the Processability
Model, closely mirror known stages of morphosyntactic devel-
opment (Pienemann, 2005). Types of inversion (do, yes/no,
Wh-copula, Wh-auxiliary, and cancel inversion) and phrasal
verb separation, for example, all appear in the correct stages. In
contrast to syntactic features, morphological features did not
follow known patterns of development as closely. The third
person singular morpheme (Processability Model: Stage 5), for
example, emerged before Wh-copula inversion (Processability
Model: Stage 4) in the predicted sequence of acquisition (Ap-
pendix D). Although features associated with the final stage of
the Natural Order (past regular, possessive -s, and third person
singular) appear correctly in the predicted sequence, features of
the other stages do not. Features of stage one (plural -s, pro-
gressive -ing, and the copula), for example, emerge in the hy-
pothesized acquisition order after the article and past irregular,
which occur in stages two and three of the Natural Order, re-
spectively.
Through review of the empirical data, the discrepancy be-
tween the prediction of syntactic and morphological features
may be explained by two key types of outliers which skew the
values of z-scores, thereby lessening the predictive validity of
the sequence. First, syntactic and lexical features have a great
deal more alternations (e.g., cancel inversion) because there are
multiple words and phrases included within the feature. The
number of alternations for both lexical features (past irregular)
and syntactic features (do-fronting, phrasal separation, and
question inversion) ranged from 7 to 1386 alternations, whereas
those for the morphological features ranged from 1 to 6. Second,
outliers for frequency appeared to skew the significance of
differences between less frequent features. Values for the arti-
cle (35,098,329) and past irregular (10,740,546) features were
both confirmed to be outliers through frequency plots. The
median value for frequency (2,575,784) is more reflective of
the overall distribution scores than the mean (4,741,198), which
has been skewed by the article and past irregular outliers.
By removing syntactic/lexical features and outliers of fre-
quency, the accuracy of morphology increases (See Appendix
E). In both the revised acquisition order for morphological fea-
tures and the Natural Order, for example, plural -s, progressive
-ing, and the copula emerge in the earliest part of the sequence,
while the past regular, possessive -s, and third person singular
emerge in the latter part of the sequence. Only the present pro-
gressive auxiliary, which had a higher value for semantic com-
plexity, emerged in an unpredictable order within the last part
of the hypothesized sequence. Through the removal of outliers,
accuracy of the predicted sequence of morphological acquisi-
tion was increased to rs = 0.694 (p = 0.083).
Discussion
Although individual causes such as frequency, sonority, com-
plexity, morphological alternations, and syntactic complexity
partially explain morphosyntactic development, their integra-
tion serves as a stronger predictor of the acquisition process.
Higher correlations between the predicted order of acquisition
and the Processability Model and Natural Order suggest that
multiple causal factors are concomitantly responsible for the se-
quences observed in historical studies. Because each causal
factor may be partly responsible for the acquisition process, an
approach to explicit instruction should utilize input and peda-
gogical techniques commensurate with causal characteristics of
each target feature.
Since morphosyntactic development can be predicted through
the synthesis of multiple causes, grammatical sequences such as
those found in the Processability Model and Natural Order
should no longer be explained away as the manifestation of an
innate, mysterious force. Results of this study reveal that the
acquisition process has concrete causes which can be both un-
derstood and modified to enhance instruction. The educator
may now work to engineer explicit grammar instruction that
hastens acquisition or promotes uniform development of mor-
phosyntactic features. Given the method of calculation within
this paper, however, features having outlying causal values can
skew the significance of other more minute disparities between
features. Syntactic (e.g., question inversion) and lexical features
(e.g., past regular), for example, have large numbers of alterna-
tions and high sonority values, which skew key differences
between less variable and less sonorant morphological features.
To increase the accuracy of predictions, syntactic and lexical
features should be separated from morphological features for
calculation.
In order to apply predictions of acquisition to practice, the
educator must develop a scale that describes appropriate in-
structional interventions for each grammatical feature. To illus-
trate how this may be accomplished, a 4-point scale was devel-
oped for the 16 morphosyntactic features analyzed within this
study. Values for each causal variable were divided into quar-
ters and assigned a scale value (0% - 25% = 4; 26% - 50% = 3;
51% - 75% = 2; 76% - 100% = 1). Ratings of 1, which are as-
signed to higher causal values that may hasten the acquisition
process, require little emphasis; ratings of 4, in contrast, are
assigned to lower causal values that may slow the acquisition
process, suggesting they require more extensive curricular em-
phasis. Due to the aforementioned influences of syntactic and
lexical outliers, ratings for syntactic/lexical and morphological
features were calculated separately. After grammatical features
were converted into the 4-point scale, causal variables of fre-
quency, alternations, semantic complexity, morphosyntactic
complexity, and sonority were paired with the corresponding
instructional interventions respectively: input, pronunciation,
visual images, grammar exercises, and listening exercises. The
results were then compiled into Table 5.
The values in Table 5 yield several insights as to how ex-

A. D. SCHENCK, W. CHOI
plicit grammar instruction should be modified to hasten acqui-
sition of selected features. First, highly sonorant features that
have a listening rating of 1, such as progressive -ing, should not
receive extensive emphasis within listening input. Those having
a listening rating of 2, in contrast, such as the progressive aux-
iliary or copula, should appear twice as often in listening dia-
logues. Features with ratings of 3 and 4 require even more em-
phasis. They should appear in listening dialogues three to four
times more often than those with a rating of 1. According to
Table 5, grammatical features with the lowest sonority, such as
the past tenses, third person singular -s, possessive -s, plural -s,
do questions, and yes/no questions, require the highest degree
of emphasis within listening and verbal input to ensure acquisi-
tion.
Second, complex syntactic features such as cancel inversion,
question inversion, and separable phrasal verbs, which have
high ratings of 3 to 4 in the grammar exercise category, should
be more highly emphasized through strategies such as focus-
on-form and written exercises that draw attention to the rela-
tionships between grammatical elements of a sentence. Com-
plex morphemes (third person singular -s, possessive -s, plural
-s, past regular, and progressive -ing) should also be substan-
tially emphasized through exercises that highlight their gram-
matical function. Overall, morphosyntactic features with ratings
of 2, 3 or 4 should respectively have 2, 3 or 4 times more
grammar exercises than those which have a rating of 1.
Third, features with high semantic complexity, such as the
article, auxiliary questions, and cancel inversion, should be ac-
companied by the largest amounts of visual stimuli (e.g., pic-
tures, videos, graphic organizers), thereby facilitating under-
standing of semantic relationships and sociolinguistic contexts.
Video conversations in a supermarket, for example, could be
used to show contexts in which the definite article is used (e.g.,
“Is this the new product you’ve been talking about?”).
Fourth, features with a large number of alternations, such as
questions, articles, the progressive auxiliary and copula, should
be emphasized highly within explicit grammar curricula. De-
liberate attempts should be made to infuse alternative forms
into aural and written input. As with the categories for listening,
grammar exercises, and visuals, features with larger pronuncia-
tion ratings should have a commensurate expansion of content.
Finally, features with the lowest frequency, such as cancel
inversion, the progressive auxiliary, and the possessive -s, should
be emphasized most extensively. Due to their rating, these fea-
tures should appear approximately four times more often than
those with a rating of 1. If normal, rather than accelerated, ac-
quisition of features is desired, frequencies commensurate with
those found in native contexts can also be infused within the
input.
As can be seen from the above recommendations, designing
grammar instruction using a scale such as that featured in Table
5 is needed. Unlike other methods of curriculum design, which
create uniform tasks for each grammatical feature via a one-
size-fits-all paradigm, this new approach tailors the curriculum
to each grammatical feature in a way that maximizes the acqui-
sition process. Although Table 5 provides useful information
for curriculum designers, it still has one major limitation. It is
designed with the assumption that all causal variables equally
influence the acquisition process. Results in this study suggest
that factors such as sonority and frequency may have a larger
influence on morphological features than other causal factors
(See Table 3). This assertion is confirmed when only values of
sonority and frequency are integrated and correlated for mor-
phological features; the resulting correlation is the best predic-
tor of the Natural Order, yielding a value that is highly signifi-
cant (rs = 0.849; p = 0.016).
While isolating the significance of causal factors is straight-
forward in some circumstances, similar correlations of causal
factors to some morphosyntactic features complicate assessments
of individual influences. Values for morphosyntactic alterna-
tions, sonority, and morphosyntactic complexity, for example,
will become larger as syntactic features grow in size. This may
explain why integrating semantic complexity, sonority, morpho-
syntactic alternations, and frequency, without the most signifi-
cant causal factor of morphosyntactic complexity, also yields
the same highly significant correlation to the Processability
Model (rs = 0.821; p = 0.007) obtained in Table 4.
Table 5.
Guide for curriculum design.
Grammar
Type
Input
(Frequency)
Pronunciation
(Alternations)
Visuals
(Semantic Complexity)
Grammar Exercises
(Syntactic Complexity) Listening (Sonority)
1. Progressive -ing 2 1 2 3 1
2. Progressive Auxiliary 4 4 3 2 2
3. Copula 2 4 2 2 2
4. Past Regular 3 3 2 3 4
5. Third Person Singular -s 2 3 2 4 3
6. Plural -s 1 3 2 3 3
7. Possessive-s 4 3 2 3 3
8. Article 1 4 4 1 2
9. Negation 2 1 2 1 1
10. Past Irregular 1 3 2 1 4
11. Separable Phrasal Verb 2 2 2 3 2
12. Do-Questions 3 1 2 3 3
13. Wh-Copula Questions 2 3 3 3 2
14. Yes/No Questions 1 2 4 3 3
15. Wh-Auxiliary Questions 3 4 4 3 1
16. Cancel Inversion 4 4 4 4 1
1 = low emphasis needed 2 = medium emphasis
needed
3 = medium high
emphasis needed 4 = high emphasis needed
120

A. D. SCHENCK, W. CHOI
Conclusion
Historical studies of morphosyntactic acquisition order could
not be pragmatically applied to education, since causes and as-
sociated effects on the acquisition process were not well known.
Although more recent research has worked to identify how
multiple causes interact to affect acquisition order, the small
scope of this research has limited its utility. Results of the cur-
rent study suggest that extending the scope of study by predict-
ing the order of a larger number of morphosyntactic features
can lead to a better understanding of the L2 acquisition process.
This understanding, in turn, may be used to modify both ESL
and EFL input in ways that promote the uniform acquisition of
multiple morphosyntactic features.
Although this study provides useful information for curricu-
lum designers, more study is needed to increase the effective-
ness of explicit grammar curricula. First, more morphosyntactic
features must be studied and combined into a comprehensive
scale. Second, the disparities of predictive validity for each
morphosyntactic feature must be further examined and refined.
Finally, the degree to which each individual causal factor in-
fluences the acquisition process must be more concretely de-
termined. Through examination of each limitation, educators
can accurately predict how reforms will impact second lan-
guage learners, thereby allowing explicit grammar curricula to
be engineered that are highly effective. Methodological reform
of curricula is particularly necessary in EFL contexts, where
limited resources and input have been shown to negatively
impact the acquisition process (Chen, 2007; Lee, 2005; Liao &
Fukuya, 2004).
Acknowledgements
I would like to express my special appreciation to Professor
Wonkyung Choi for serving as a corresponding author on this
project. I would also like to thank my wife Jinny, son Matt, and
daughter Katie for their patience and understanding, without
which I could not have completed this paper.
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A. D. SCHENCK, W. CHOI
Appendix A
Table A1.
Grammar features, corpus search strings, and frequencies.
Plural (-s, -es)
*s.[n] POS List noun.PL 7,459,308
Singular Copula ( is, ‘s)
is -[v] 2,382,962
's.[v] -[v] 1,298,254
Progressive (- ing)
[v?g*](includes non prog elements) 4, 237, 206
Progressive Auxiliary (is, ‘s)
is (collocate) *ing.[v] 417, 714
's.[v] *ing.[v] 341, 157
Past Regular
*ed.[v?d*] POS List verb.ED 2, 575, 784
Past Irregular
-*ed.[v?d*] POS List verb.ED 10, 740, 546
Possessive ('s)
[n] 's 677,015
Third Per son Singular -s
[v?z*] 10, 371, 795
subtract -is 3, 987, 516
subtract –’s 2, 016, 509
subtract -has 1, 130, 455
subtract -does 347, 046
Total: 2, 890, 269
Article (a, an, the)
a|an|the 35, 098, 329
Particle Verbs
[v*] [n*] [in|into|at|on|up|down|off|under|out|over|back|around|about 19,
162
[v*] [n*] over|through|with|without|away|across|for|to|after|for 73,
154
Total: 92, 316
Negation + Verb
Not 1, 784, 767
No 833, 269
TOTAL: 2, 618, 036
Do-questions
.|;|:|,|" do [pp*]|[n*] 69, 779
Yes/No Inversion
.|;|:|,|" do|does|did|will|would|can|could|should|have|had|has|must|might
[pp*]|[n*] 165, 855
Wh-Copula Inversion
1. what|when|how|why|where|who|whom|whose [vb*] [pp*]|[n*] 79, 511
2. how long|many|much [vb*] [pp*]|[n*] 1, 215
TOTAL: 80, 726
Wh-Auxiliary Inversion
1. what|when|how|why|where|who|whom|whose
do|does|did|will|would|can|could|should|have|had|has|must|might
[pp*]|[n*] [v*] 33, 889
2. how long|many|much
do|does|did|will|would|can|could|should|have|had|has|must|might
[pp*]|[n*] [v*] 3, 606
3. what|when|how|why|where|who|whom|whose [vb*] [pp*]|[n*] *ing.[v]
10, 145
4. how long|many|much [vb*] [pp*]|[n*] *ing.[v] 419
TOTAL: 48, 059
Wh Do-fronting
1. what|when|how|why|where|who|whom|whose do [pp*]|[n*] [v*] 57, 259
2. how long|many|much do [pp*]|[n*] [v*] 1, 371
TOTAL: 58, 630
Cancel Inversion 1.
if|what|when|how|why|where|who|whom|whose [n] * [v*] 3, 971
how long|many|much [n] * [v*] 1, 411
TOTAL: 5, 382
Appendix B
Table B1.
Categories of wh-aux question types.
Interrogatives
(Master, 1996: p. 141)
Auxiliary
(Master, 1996: p. 12)
Subject Pronouns
(Master, 1996: p. 149)
What Do I
When Does You
Where Did He
Who Will She
Whom Would It
Whose Can They
Why Could We
How Should
How long Have
How many Had
How much Has
Must
Might
Is (Progressive)
Am (Progressive)
Are (Progressive)
Was (Progressive)
Were (Progressive)
Table B2.
Sonority scale.
Sound Point Value Examples
Low Vowels 12 a, æ
Mid Vowels 11 e, o
High Vowels 10 i, u
Glides 9 w, y
Flaps 8 r
Laterals 7 l
Nasals 6 m, n, ŋ
Voiced Fricative 5 v, z, ð
Voiceless Fricative 4 f, s, θ, h, ʃ
Affricate 3 t ̬ʃ, dʒ
Voiced Stop 2 b, d, g
Voiceless Stop 1 p, t, k
Appendix C
Table C1.
Semantic complexity calculation (Adapted from Brown, 1973).
Morpheme Meanings
1. Progressive -ing
2. Plural
3. Past Irregular
4. Past Regular
5. Possessive
6. Present Copula
7. Article
8. Third Person Singular -s
9. Present Progressive Auxil-
iary
10. Negation (No/Not)
11. Do-fronting
12. Phrasal Verb
13. Wh Copula Question
14. Yes/No Question
15. Wh Auxiliary Question
16. Cancel Inversion
Temporary duration
Number
Earlierness
Earlierness
Possession
Number
Specific-nonspecific; com-
mon/proper nouns; mass/count
nouns; generic statements
Number
Temporary duration; number
Negation
Question
Earlierness; number; future; tempo-
rary duration
Question; earlierness; number;
future
Question; earlierness; number;
future; Temporary duration
Question; earlierness; number;
future; Temporary duration
Question; earlierness; number;
future; Temporary duration

A. D. SCHENCK, W. CHOI
124
Table C2.
Complexity for morphological and syntactic features.
Syntactic Categories Points
Lexical
Free 1
Bound 2
Functional
Free 3
Bound 4
Inter-phrasal 5
Inter-sentential 6
Appendix D
Table D1.
Predicted sequence of acquisition for all features.
Morphosyntactic Feature Z Score Value
1. Past irregular 0.82
2. Article 0.68
3. Negation 0.31
4. Is Copula Combined 0.19
5. ING 0.17
6. Plural -s 0.16
7. Past regular 0.03
8. Do questions 0.02
9. Is Prog Combined 0.01
10. Poss s 0.01
11. Third person singular –0.10
12. Wh Copula –0.14
13. Phrasal verb separated –0.25
14. Yes/no aux questions –0.39
15. Wh aux questions –0.69
16. Cancel Inversion –0.86
Appendix E
Table E1.
Morphological features (Syntactic, lexical, and frequency outliers re-
moved).
Morphosyntactic Feature Z Score Value
1. Negation 0.83
2. Progressive -ING 0.75
3. Plural -s 0.28
4. Is Copula 0.05
5. Past Regular –0.31
6. Possessive -s –0.35
7. Third Person Singular –0.48
8. Is Progressive –0.78
Table E2.
Correlations to the natural order (syntactic, lexical, and frequency out-
liers removed).
Predicted Sequence of Acquisition
r 0.694
p 0.083
Natural Order
N 7