Natural Order Hypothesis

The Natural Order Hypothesis (Krashen 1982, building on Dulay & Burt 1974) claims that grammatical structures are acquired in a predictable sequence, and this order is largely independent of the order in which structures are taught.

The Evidence: Morpheme Order Studies

In the 1970s, researchers studied the order in which L2 English learners produced certain grammatical morphemes accurately. The findings were remarkably consistent across L1 backgrounds:

Acquired early:

• Progressive -ing (she is running)
• Plural -s (two cats)
• Copula be (he is tall)

Acquired in the middle:

• Auxiliary be (she is running)
• Articles (a, the)

Acquired late:

• Irregular past (went, saw)
• Regular past -ed (walked)
• Third person -s (she walks)
• Possessive -s (John's)

The order for L2 learners is similar but not identical to the L1 acquisition order. Crucially, it appears to be relatively stable regardless of the learner's first language or the order of classroom instruction.

Why It Matters

The implications are significant and uncomfortable for traditional grammar syllabuses:

• Teaching order does not equal acquisition order. A textbook may introduce the simple past in Unit 3, but learners may not truly acquire it until much later, regardless of how well they perform on the Unit 3 test.
• Errors are developmental, not deficient. A learner who says "she walk" is not being careless — they may simply not have reached the acquisition stage for third person -s. This aligns with Interlanguage theory.
• Structured syllabuses may be inefficient. If acquisition follows its own order, rigidly sequenced grammar teaching may not accelerate it.

Criticisms

• Accuracy order vs acquisition order. The studies measured accuracy of production in obligatory contexts, not the actual moment of acquisition. These may not be the same thing.
• Limited to morphemes. The research focused on a small set of English grammatical morphemes. It does not clearly extend to syntax, vocabulary, or phonology.
• Does not mean teaching is useless. The hypothesis is sometimes misinterpreted as "don't teach grammar." Krashen himself argued that teaching grammar has value for monitoring (editing output), even if it does not change the natural order. More importantly, Focus on Form research shows that drawing attention to forms during communicative activities can accelerate movement through developmental stages.
• Individual variation exists. While the general order is robust, there is meaningful variation between individuals, especially at intermediate stages.

Practical Takeaways

• Do not panic when learners make errors on structures you have "already taught" — developmental readiness matters
• Expose learners to rich, varied input rather than limiting it to "today's grammar point"
• Recycle structures repeatedly across lessons rather than assuming one teaching cycle is enough
• Use Formative Assessment to track what learners are actually acquiring, not just what they can reproduce on controlled exercises