Natural Order Hypothesis

Definition:

The Natural Order Hypothesis is one of five hypotheses in Stephen Krashen‘s Monitor Model of second language acquisition. It proposes that grammatical structures and morphemes are acquired in a largely predictable, universal sequence — independent of the learner’s native language, the order in which structures are taught by a teacher or textbook, or the learner’s age. This natural order is not random but reflects an internal developmental logic: some structures are reliably acquired before others across learners from diverse L1 backgrounds and instructional contexts. The hypothesis has both descriptive significance (documenting the universal sequences) and pedagogical significance (challenging the assumption that teaching structures in any arbitrary sequence will result in acquisition in that sequence).

Also known as: the natural order of acquisition, the morpheme order studies tradition, developmental sequences

In-Depth Explanation

Origin: the morpheme order studies.

The Natural Order Hypothesis was informed by a series of empirical studies in the 1970s that investigated the order in which English grammatical morphemes are acquired by L1-acquiring children and by L2 learners:

• Brown (1973): Longitudinal study of three English L1 children showing that 14 grammatical morphemes (articles, plural -s, possessive -s, progressive -ing, past tense -ed, etc.) were acquired in a consistent sequence across all three children.

• Dulay and Burt (1974, 1975): Cross-sectional studies of L2 English learners from Spanish and Chinese L1 backgrounds found a consistent accuracy order for English grammatical morphemes — largely similar to the L1 acquisition order identified by Brown — and not significantly predicted by the learner’s L1. This challenged the Contrastive Analysis Hypothesis’s prediction that L1-L2 differences should dominate acquisition difficulty.

• Bailey, Madden, and Krashen (1974): Further confirmed a consistent morpheme accuracy order for adult L2 English learners.

Krashen interpreted these morpheme accuracy orders as reflecting an underlying acquisition order — the natural sequence in which the brain builds up grammatical competence.

The claimed natural order for English morphemes.

The approximate natural order for English grammatical morphemes (from earlier to later acquired):

1. Progressive -ing (I am eating) and plural -s (two cats)
2. Copula be (he is tall)
3. Articles the/a
4. Irregular past (he went)
5. Regular past -ed (he walked)
6. Third-person singular -s (he eats)
7. Possessive -s (John‘s book)

Note that regularized forms (regular past -ed, third-person -s) are acquired later than their irregular counterparts — a finding consistent with the U-shaped development of irregular morphology discussed in Overgeneralization.

Pedagogical implications.

Krashen drew a strong pedagogical conclusion from the Natural Order Hypothesis:

• Teachers cannot change the natural order by teaching structures in a different sequence.
• Teaching a structure before the learner is developmentally ready to acquire it will not result in acquisition, only temporary learned performance.
• This supports the argument for meaning-focused input rather than grammatically-sequenced instruction as the primary driver of acquisition — the grammar will emerge in its natural order as long as comprehensible input is provided.

This position is related to the Teachability Hypothesis proposed by Manfred Pienemann (1984, 1998): learners can only acquire structures they are developmentally ready for, and instruction can only advance acquisition of the next stage in the sequence, not skip stages.

Critique and empirical complications.

The Natural Order Hypothesis, while capturing important regularities, faces several challenges:

1. Accuracy ? acquisition order: The morpheme studies measured accuracy in production (what percentage of obligatory contexts featured the correct morpheme), not necessarily acquisition (permanent internalization). Accuracy order may reflect processing difficulty rather than developmental sequence.

1. Instruction effects: Research by Pica (1983) and others showed that the morpheme order is somewhat different for learners in formal instructional contexts compared to naturalistic acquisition — formal instruction can shift some features in the sequence, challenging the universality claim.

1. Individual and L1 variation: While the general order shows cross-L1 consistency, specific language pairs show L1-specific modification. The claim of strict universality overstates the consistency.

1. Limited scope: The morpheme order studies focused on a small set of English grammatical morphemes. The Natural Order Hypothesis is difficult to extend rigorously to syntax, phonology, or non-English target languages.

Natural Order and Japanese.

For Japanese learners, analogues to the Natural Order Hypothesis have been investigated:

• Japanese particle acquisition (?, ?, ?, ?, ?) shows consistent developmental patterns across learners.
• Japanese verb forms: ?-form tends to be acquired earlier than conditional forms; plain form earlier than keigo (formal) forms.
• The implication for Japanese learners: the natural processing sequence of Japanese grammar — rather than the textbook’s organizational order — should inform the priority and timing of grammar study.

Common Misconceptions

“You should never teach grammar because it disrupts the natural order.”

Krashen’s position does not imply grammar should never be taught — it implies that explicit grammar teaching produces learned knowledge, not acquired competence, and that the sequence of instruction does not determine the sequence of acquisition. Focused grammar attention — particularly focus on form approaches — is compatible with natural order thinking when it targets forms the learner is developmentally approaching.

“All learners acquire morphemes in exactly the same order.”

The natural order is a statistical tendency, not a universal law. The morpheme studies show consistent group tendencies with substantial individual variation. Individual learners deviate from the group order for specific morphemes based on their learning history, L1, and instructional context.

Criticisms

The Natural Order Hypothesis has been extensively critiqued for circular reasoning — the “natural order” is derived from accuracy studies, but accuracy order may reflect processing difficulty, L1 transfer, or input frequency rather than an innate acquisition sequence. Cross-linguistic evidence is inconsistent, with acquisition orders varying by L1 background. The hypothesis is also criticially underspecified — it does not predict why a particular order exists or what mechanism drives it, making it descriptive rather than explanatory.

Social Media Sentiment

The Natural Order Hypothesis occasionally surfaces in language learning communities when learners ask whether they should study grammar in a particular order. The concept reassures learners that making certain errors is developmentally normal. However, most practical language learning discussions do not reference the hypothesis explicitly, as it is more relevant to theoretical SLA than to study planning.

Last updated: 2026-04

History

The Natural Order Hypothesis was proposed by Krashen based on his synthesis of the morpheme order studies in a series of papers from the mid-1970s, culminating in his Monitor Model texts (1981, 1982). The foundational empirical studies were Roger Brown’s (1973) L1 morpheme study and Dulay and Burt’s (1974, 1975) L2 morpheme studies. Pienemann’s Processability Theory (1998) extended the developmental sequence framework most rigorously beyond the morpheme level.

Practical Application

• Understand that grammar acquisition tends to follow predictable sequences regardless of teaching order — some structures will take longer to master than others
• Don’t be discouraged by persistent errors with certain grammar points (e.g., English third-person -s) — these are known to be late-acquired
• Use the natural order concept to set realistic expectations rather than as a rigid curriculum guide
• For self-study, follow textbook grammar sequences (which are roughly aligned with difficulty) while accepting that mastery will follow its own timeline
• Focus on communicative practice rather than trying to force mastery of structures your developmental level may not support yet

Related Terms

• Stephen Krashen
• Acquisition-Learning Distinction
• Interlanguage
• Overgeneralization

See Also

• Affective Filter Hypothesis
• Monitor Hypothesis
• Input Hypothesis
• Focus on Form

• Sakubo

Research

1. Krashen, S.D. (1977). Some issues relating to the Monitor Model. In H. Brown, C. Yorio, & R. Crymes (Eds.), On TESOL ’77. Washington: TESOL.

— Krashen’s initial synthesis of morpheme order research into the Natural Order Hypothesis, the founding paper of the Monitor Model tradition.

1. Dulay, H.C., & Burt, M.K. (1974). Natural sequences in child second language acquisition. Language Learning, 24, 37–53.

— Key empirical study demonstrating a consistent morpheme accuracy order for L2 English learners from Chinese and Spanish L1 backgrounds; foundational evidence for the Natural Order Hypothesis.

1. Pica, T. (1983). Adult acquisition of English as a second language under different conditions of exposure. Language Learning, 33, 465–497.

— Found that formal instruction modifies the morpheme order somewhat compared to naturalistic acquisition — challenging the strict universality claim while confirming the general developmental sequence tendencies.

1. Pienemann, M. (1998). Language Processing and Second Language Development: Processability Theory. Amsterdam: John Benjamins.

— The most rigorous theoretical extension of the natural order concept; Processability Theory explains developmental sequences as reflecting the processing prerequisites learners must master before higher-stage structures can be acquired.

1. Brown, R. (1973). A First Language: The Early Stages. Cambridge, MA: Harvard University Press.

— The L1 acquisition study that initiated the morpheme order research tradition; documented the consistent order of English morpheme acquisition across three children, providing the L1 benchmark against which Dulay and Burt’s L2 data were compared.