The Natural Order Hypothesis: Why We Learn Grammar in a Predictable Sequence
The natural order hypothesis is one of the most important ideas in language learning, yet many learners and teachers still assume that grammar should be taught from “simple” to “complex.” Start with the present tense, then move to past tense, then tackle the subjunctive. This sequencing seems logical. However, decades of research suggest that learners acquire grammatical structures in a fixed order that does not match any textbook sequence.
This finding is the core of Stephen Krashen‘s Natural Order Hypothesis, one of the five hypotheses in his theory of second language acquisition. Understanding this hypothesis changes how you approach grammar, what you expect from your study routine, and how you evaluate your own progress.
What the Natural Order Hypothesis Claims
Krashen first articulated the Natural Order Hypothesis in the late 1970s and formalized it in Principles and Practice in Second Language Acquisition (1982, Pergamon Press). The hypothesis states that learners acquire the grammatical structures of a second language in a predictable order. This order is largely independent of the order in which structures are taught in the classroom.
In other words, even if a teacher drills the third person singular -s (he walks, she talks) in week one and the progressive -ing (he is walking, she is talking) in week ten, learners will still acquire -ing before -s. Teaching order does not determine acquisition order. Something internal to the learner does.
This claim is bold. It implies that much of traditional grammar instruction may be mistimed, teaching structures before learners are ready to acquire them and delaying structures that learners could pick up naturally earlier.
The Evidence: Morpheme Studies
The Natural Order Hypothesis is grounded in a series of studies on the order in which learners acquire English grammatical morphemes. These morphemes are small grammatical markers like plural -s, past tense -ed, articles (a, the), and auxiliary verbs.
The Brown Study (1973)
Roger Brown’s landmark study (1973, A First Language: The Early Stages, Harvard University Press) tracked the acquisition of 14 grammatical morphemes in three children learning English as their first language. Brown found a consistent acquisition order. For example, the progressive -ing and the plural -s were acquired early, while the third person singular -s and the possessive -s were acquired late.
Brown’s study focused on first language acquisition. The question was whether second language learners followed a similar pattern.
Dulay and Burt (1973, 1974)
Heidi Dulay and Marina Burt conducted foundational studies on second language morpheme acquisition in children. In their 1974 study (“Natural sequences in child second language acquisition,” Language Learning), they examined 250 children from Spanish and Chinese language backgrounds learning English.
Their results were striking. Children from both language backgrounds acquired English morphemes in a remarkably similar order. This consistency across different first languages suggested that the acquisition order was driven by properties of English itself, or by universal cognitive processes, rather than by transfer from the first language.
Dulay and Burt found that morphemes like the progressive -ing, the plural -s, and the copula “be” (she is happy) were acquired early. Articles (a, the), the irregular past tense (went, came), and the auxiliary “be” (she is running) came in the middle. The third person singular -s (he runs), the possessive -s (John’s), and the regular past tense -ed were acquired late.
Bailey, Madden, and Krashen (1974)
Bailey, Madden, and Krashen (1974, “Is there a ‘natural sequence’ in adult second language learning?” Language Learning) extended the morpheme studies to adult learners. They tested 73 adult ESL learners from various first language backgrounds and found an acquisition order very similar to the one Dulay and Burt identified in children.
This finding was significant because it suggested the natural order applies to adults, not just children. Furthermore, the adult order showed similarities to Brown’s first language acquisition order, though the two were not identical. The parallel suggested that some fundamental cognitive mechanism drives grammatical acquisition regardless of age.
Krashen’s Synthesis
Krashen synthesized these studies and others into the Natural Order Hypothesis. He proposed a general acquisition order for English morphemes:
Acquired early:
- Progressive -ing (I am reading)
- Plural -s (two books)
- Copula “be” (She is tall)
Acquired in the middle:
- Auxiliary “be” (He is running)
- Articles a, the
- Irregular past tense (went, saw, came)
Acquired late:
- Regular past tense -ed (walked, talked)
- Third person singular -s (she walks)
- Possessive -s (Maria’s book)
Notice something counterintuitive: the regular past tense -ed is acquired after the irregular past tense. Learners say “went” correctly before they consistently say “walked.” They also produce “she walk” long after they know the rule for adding -s. Knowing a rule and having acquired a structure are fundamentally different things.
Why Grammar Sequence Does Not Match Learning Sequence
Traditional grammar syllabi sequence structures by perceived simplicity or communicative usefulness. However, the natural order evidence suggests that internal readiness, not external sequencing, determines when a structure is truly acquired.
Pienemann (1984, “Psychological constraints on the teachability of languages,” Studies in Second Language Acquisition) developed the Teachability Hypothesis, which directly addresses this point. Pienemann proposed that instruction can only promote acquisition when the learner is developmentally ready for the next stage. Teaching a structure too early has no lasting effect because the learner’s processing capacity cannot yet handle it.
This does not mean grammar instruction is useless. Rather, it means instruction is most effective when it targets structures the learner is ready to acquire. Instruction that is well-timed can accelerate acquisition. Instruction that is premature will not stick, regardless of how clearly it is explained or how much it is drilled.
For self-directed learners, this finding has practical implications. If you have studied a grammar rule, understand it perfectly on paper, but consistently fail to apply it in conversation, you are likely not yet ready to acquire that structure. Continue with meaningful input, and the structure will emerge when your internal system is ready language learning consistency tips.
Connection to Comprehensible Input
The Natural Order Hypothesis is closely linked to Krashen’s Input Hypothesis, which states that we acquire language by receiving “comprehensible input” that is slightly beyond our current level. Krashen calls this “i+1,” where “i” represents the learner’s current competence and “+1” represents the next natural step.
The connection works as follows: if there is a natural order, then at any point in your learning, there are specific structures you are ready to acquire next. Comprehensible input at the i+1 level naturally contains these structures. You do not need to identify or target them explicitly. By simply engaging with meaningful, slightly challenging input, you encounter the structures your brain is primed to absorb.
Krashen argues in The Input Hypothesis: Issues and Implications (1985, Longman) that this is precisely how first language acquisition works. Children do not learn grammar through explicit instruction. They acquire it through massive exposure to comprehensible input from caregivers and their environment. The Natural Order Hypothesis suggests second language acquisition follows a similar pattern, even though the specific order may differ slightly from first language acquisition.
For practical purposes, this means that extensive reading and listening are not just supplements to grammar study. They are arguably the primary mechanism through which grammatical structures are acquired. Reading at an appropriate level provides a steady stream of comprehensible input containing structures at and just beyond your current level learn french through reading.
Criticisms and Nuances
The Natural Order Hypothesis is not without criticism. Understanding the limitations helps you apply the concept more effectively.
Methodological Concerns
Many morpheme studies relied on the Bilingual Syntax Measure (BSM), a specific testing instrument. Some researchers, including Rosansky (1976, “Methods and morphemes in second language acquisition research,” Language Learning), questioned whether the BSM accurately reflected acquisition as opposed to test-taking strategies. Different testing methods sometimes produced different orders, raising questions about how robust the “natural order” truly is.
Order vs. Sequence
The hypothesis describes a general order, not a strict sequence. Learners do not fully master one morpheme before beginning to acquire the next. Instead, multiple structures develop simultaneously, with some reaching accuracy earlier than others. The “order” is a tendency observed across groups, not a rigid timeline for individual learners.
First Language Influence
While Dulay and Burt found similar orders across language backgrounds, subsequent research has identified some first language effects. Learners whose first language has a similar structure may acquire that structure somewhat earlier. However, these effects appear to modify the order at the margins rather than overriding it entirely.
Beyond English
Most morpheme studies focused on English. Evidence for a natural order in other target languages is less extensive. Research by Johnston (1985, “Syntactic and morphological progressions in learner English,” Department of Immigration and Ethnic Affairs) and others has identified developmental sequences in languages including German and Swedish. However, the claim that a single universal order governs all language acquisition is stronger than the evidence currently supports. The more defensible claim is that learners of a given language follow a roughly predictable sequence.
Practical Takeaways for Language Learners
Understanding the Natural Order Hypothesis leads to several actionable strategies.
1. Do Not Panic About Grammar Errors
If you consistently make a particular grammar error despite knowing the rule, you have likely not yet acquired that structure. This is normal and expected. Continued exposure to comprehensible input will eventually lead to acquisition. Excessive self-correction and anxiety about specific errors can actually impede the natural acquisition process by increasing what Krashen calls the “affective filter.”
2. Prioritize Input Over Drills
Grammar drills have their place, particularly for raising awareness of structures. However, drills alone do not produce acquisition. Extensive reading and listening to meaningful content at an appropriate level do more for grammatical accuracy over time than isolated grammar exercises.
TortoLingua’s reading-based approach aligns with this principle by providing level-appropriate texts that expose learners to grammatical structures in natural context, supporting the acquisition process as described by the Input Hypothesis how reading helps language learning.
3. Trust the Process
If you are consistently engaging with comprehensible input, grammatical structures are being acquired even when you cannot see the progress. Acquisition is largely subconscious. You may suddenly realize you are using a structure correctly without ever having consciously studied it. This experience, which many language learners report, is exactly what the Natural Order Hypothesis predicts.
4. Use Grammar Study Strategically
Grammar instruction is most useful as a way to notice structures in input. When you study a grammar point, you become more likely to notice it when reading or listening. This “noticing” function, described by Schmidt (1990, “The role of consciousness in second language learning,” Applied Linguistics), may facilitate acquisition by drawing attention to structures the learner is ready to process.
Therefore, study grammar to raise awareness, then engage with input to encounter those structures in context. Do not rely on grammar study alone to produce accurate output.
5. Sequence Your Study Flexibly
If your textbook presents grammar in a particular order and you find certain structures sticking while others do not, adjust your focus accordingly. Spend more time on input that contains the structures you are naturally acquiring, and do not force structures that are not ready to emerge. Return to difficult structures periodically, and you may find they have become easier due to overall language growth.
The Natural Order in Other Languages
While most research has focused on English, the general principle applies across languages. Each target language has its own developmental sequence that learners tend to follow.
For example, learners of German follow a predictable sequence in acquiring word order rules, moving from simple subject-verb-object patterns to verb-second main clauses to subordinate clause structures. Learners of Spanish acquire subjunctive mood uses in a predictable order, with doubt expressions before desire expressions before hypotheticals.
If you are learning any language, expect that some grammar points will click quickly while others resist despite repeated study. This variation reflects the natural order at work, not a deficiency in your learning ability serbian for beginners guide.
Implications for Self-Study and Apps
Modern language learning apps and self-study programs vary in how well they accommodate the natural order. Programs that emphasize massive comprehensible input (through reading and listening) tend to align well with natural acquisition processes. Programs that force a rigid grammar sequence and expect mastery before moving on may conflict with how acquisition actually works.
When choosing tools and methods, consider these questions:
- Does the program provide large amounts of comprehensible input at my level?
- Does it allow me to encounter grammar in context rather than only through isolated rules?
- Does it tolerate errors on structures I have not yet naturally acquired?
- Does it expose me to varied, meaningful content rather than repetitive pattern drills?
Programs that score well on these criteria are more likely to support natural acquisition than those that follow a strict grammar-first approach.
Bringing It All Together
The Natural Order Hypothesis offers a powerful reframe for language learners. Grammar acquisition is not a matter of willpower, intelligence, or study hours alone. It follows a developmental path that your brain navigates on its own schedule, driven primarily by exposure to comprehensible input.
Your job as a learner is not to force the order. It is to provide the raw material: consistent, meaningful, level-appropriate input through reading, listening, and interaction. The grammar will come. It may not come in the order your textbook prescribes, and that is perfectly fine. Trust the process, stay consistent, and let your brain do what it has evolved to do: acquire language naturally language learning consistency tips.