Monitor Model

Definition:

The Monitor Model is a comprehensive theory of second language acquisition (SLA) developed by Stephen Krashen between 1977 and 1985. It describes language acquisition through five interconnected hypotheses, arguing that natural, unconscious acquisition through comprehensible input — not explicit grammar instruction — is the primary driver of second language development.

In-Depth Explanation

The Monitor Model is Stephen Krashen‘s attempt to provide a unified theoretical account of how adults acquire second languages. It integrates five hypotheses that together describe the mechanisms of acquisition, the role of conscious learning, the sequence of development, the input conditions that drive acquisition, and the emotional factors that facilitate or block it.

The Five Hypotheses:

1. Acquisition-Learning Hypothesis: Krashen distinguishes two independent systems for developing second language competence. Acquisition is an implicit, unconscious process identical to how children acquire their first language — through meaningful communication. Learning is an explicit, conscious process: the deliberate study of grammar rules and forms. The key claim is that these are separate systems: learned knowledge cannot be “converted” into unconscious acquired knowledge. Only acquired knowledge drives fluent language use.

1. Monitor Hypothesis: Consciously learned grammar serves only as a “Monitor” — an internal editor that checks and corrects output after it is generated by the acquired system. Using the Monitor requires three conditions: time to reflect, focus on form (not meaning), and knowledge of the relevant rule. Over-reliance on the Monitor (over-monitoring) can impair fluency by interrupting the natural flow of acquired language.

1. Natural Order Hypothesis: Grammatical morphemes are acquired in a predictable sequence across learners, regardless of their first language or the order in which forms are taught. English learners, for example, tend to acquire the progressive (-ing), plural (-s), and copula (is/are) before the third-person singular (-s) and auxiliary verbs. This suggests acquisition follows its own internal timetable not easily altered by instruction.

1. Input Hypothesis: Language is acquired through exposure to comprehensible input slightly above the learner’s current level (i+1). This is the central acquisitional mechanism — the engine that drives progress through the natural order. Krashen argues that when input is comprehensible and provided in sufficient quantities, acquisition occurs naturally without explicit study.

1. Affective Filter Hypothesis: Emotional factors — anxiety, motivation, and self-confidence — create a metaphorical “filter” that modulates how much input is processed for acquisition. A low affective filter (high motivation, low anxiety) allows input to reach the language acquisition device effectively. A high filter (anxiety, low confidence) blocks input even when it is comprehensible. This hypothesis has implications for classroom environment, teacher approach, and the psychological design of language learning tools.

Together, the five hypotheses form a coherent framework that shifted language teaching attention away from grammar drills and error correction toward meaningful communication, extensive reading and listening, and creating low-anxiety learning environments. The Natural Approach and communicative language teaching both draw heavily on the Monitor Model.

The model has attracted substantial criticism. Critics argue the acquisition-learning distinction is unfalsifiable (Barry McLaughlin, 1978), that the Monitor’s conditions are too restrictive (Gregg, 1984), and that the model fails to adequately account for the role of output and interaction in acquisition (Merrill Swain, 1985; Long, 1996). These critiques have driven the development of the Output Hypothesis, Interaction Hypothesis, and other models that complement or challenge Krashen’s framework.

History

• 1977: Krashen introduces the acquisition-learning distinction at a TESOL conference, providing the foundational claim around which the entire Monitor Model will be built. [Krashen, 1977]

• 1978: Barry McLaughlin publishes a critique of the Monitor Model, arguing the acquisition-learning distinction lacks an adequate psychological basis and that the model’s predictions are untestable. Despite this, the model continues to gain influence. [McLaughlin, 1978]

• 1982: Principles and Practice in Second Language Acquisition presents the full Monitor Model for the first time. The book becomes one of the most cited works in applied linguistics and directly transforms teacher training programs and curriculum design worldwide. [Krashen, 1982]

• 1983: The Natural Approach (with Terrell) provides a practical classroom methodology derived from the Monitor Model, emphasizing comprehensible input, meaning-focused communication, and low-anxiety environments. [Krashen & Terrell, 1983]

• 1984–1985: Kevin Gregg publishes the most influential critique of the Monitor Model. Merrill Swain publishes the Output Hypothesis, challenging the model’s claim that input alone is sufficient. Both critiques initiate productive theoretical debates that drive SLA research forward. [Gregg, 1984; Swain, 1985]

• 1985: Krashen publishes The Input Hypothesis: Issues and Implications, the most detailed treatment of hypotheses 4 and 5 in explicit response to critiques. [Krashen, 1985]

• 1990s–present: The Monitor Model loses some theoretical prominence as newer frameworks (emergentism, usage-based linguistics, sociocognitive approaches) gain currency. However, its influence on language teaching practice largely persists. The comprehensible input movement, graded readers, language immersion programs, and many popular language learning apps continue to operate on Monitor Model principles.

Common Misconceptions

“The Monitor Model and the Input Hypothesis are the same thing.”

The Monitor Model is the overarching theory comprising five interconnected hypotheses: the Acquisition-Learning Distinction, the Monitor Hypothesis, the Natural Order Hypothesis, the Input Hypothesis (i+1), and the Affective Filter Hypothesis. The Input Hypothesis is the best-known component but does not represent the full model.

“Krashen says grammar should never be taught.”

Krashen argues that explicit grammar instruction feeds the Monitor (conscious knowledge) rather than the acquisition system — but he acknowledges that the Monitor has a limited, useful role in editing output for accuracy. His position is that grammar instruction should not be the primary activity, not that it should be entirely absent.

“The Model has been discredited and abandoned.”

While specific components — particularly the acquisition-learning distinction and the unfalsifiability of i+1 — have been heavily critiqued, the Monitor Model’s influence on language teaching practice remains enormous. The emphasis on comprehensible input, low-anxiety environments, and meaning-focused instruction is broadly supported by subsequent research, even as the theoretical mechanisms Krashen proposed remain contested.

“Acquired knowledge and learned knowledge are completely separate systems.”

This is Krashen’s own claim, but it is among the most criticized components of the model. Most current SLA researchers support some form of interface position — that explicit and implicit knowledge interact, with explicit knowledge potentially facilitating implicit acquisition under certain conditions.

Criticisms

The Monitor Model has attracted more sustained academic criticism than any other SLA theory. Gregg (1984) argued that the acquisition-learning distinction is unfalsifiable — since Krashen provides no independent diagnostic for determining whether knowledge is “acquired” or “learned,” the hypothesis cannot be tested. McLaughlin (1987) critiqued the entire model as a collection of interconnected hypotheses that are individually unfalsifiable and jointly circular.

The i+1 construct has been criticized for being impossible to operationalize: there is no established measure of “i” (current competence level) precise enough to define what “+1” means in practice. Merrill Swain‘s Output Hypothesis provided direct empirical challenge — Canadian immersion students with thousands of hours of comprehensible input still exhibited persistent grammatical gaps, demonstrating that input alone is insufficient. The Affective Filter Hypothesis has been criticized as a metaphor rather than a mechanism — it describes the observation that anxiety impairs learning without explaining the cognitive process involved.

Despite these criticisms, the Model’s practical influence on communicative language teaching, extensive reading programs, and input-based methodologies has been enormous and largely positive.

Social Media Sentiment

The Monitor Model, primarily through Stephen Krashen‘s public advocacy, has significant cultural presence in online language learning communities. Krashen’s YouTube lectures and podcast appearances have made him one of the most recognizable figures in the field. The “comprehensible input” concept derived from the model is treated as foundational by immersion-based communities (Refold, AJATT derivatives).

Debates about the Monitor Model frequently occur in r/languagelearning and r/LearnJapanese, typically between input-only advocates who cite Krashen and learners who argue for explicit grammar study alongside input. The model’s popularity among practitioners despite academic criticism is a recurring discussion topic.

Practical Application

The Monitor Model’s practical implications, while debated, offer useful guidance:

1. Prioritize comprehensible input — Regardless of theoretical disputes, the evidence strongly supports that extensive exposure to understandable target language material drives acquisition. Structure study around extensive reading and listening.
2. Reduce anxiety in production — The Affective Filter concept, even if theoretically imprecise, correctly identifies that high-anxiety environments impair language use. Practice speaking in low-stakes contexts before high-pressure situations.
3. Use grammar knowledge as an editor, not a generator — When writing, use explicit grammar knowledge to check and correct output. In spontaneous speech, trust acquired patterns rather than trying to consciously apply rules in real time.
4. Don’t rely solely on input — Post-Krashen research demonstrates clear benefits from some explicit instruction, output practice, and focus on form. The Monitor Model is most useful when supplemented rather than followed exclusively.

For Japanese learners, Sakubo provides the vocabulary foundation that makes subsequent input comprehensible — building the lexical knowledge through which the Monitor Model’s input-based acquisition can operate.

Related Terms

• Comprehensible input
• Input Hypothesis
• Output Hypothesis
• Stephen Krashen
• Pedagogy

See Also

• Merrill Swain
• SRS (Spaced Repetition System)
• Cognitive load

• Sakubo

Research

• Krashen, S. (1982). Principles and Practice in Second Language Acquisition. Pergamon Press. https://www.sdkrashen.com/content/books/principles_and_practice.pdf
  Summary: The primary source — the most complete presentation of all five Monitor Model hypotheses. The most widely cited reference for understanding Krashen’s full theoretical framework and its implications for language teaching.

• Krashen, S. (1985). The Input Hypothesis: Issues and Implications. Longman.
  Summary: Krashen’s extended treatment of hypotheses 4 and 5 (Input and Affective Filter), responding to critiques and applying the model to curriculum design and reading instruction.

• McLaughlin, B. (1978). The Monitor Model: Some methodological considerations. Language Learning, 28(2), 309–332. https://doi.org/10.1111/j.1467-1770.1978.tb00137.x
  Summary: An early and influential methodological critique of the Monitor Model, arguing the acquisition-learning distinction lacks an adequate psychological basis. Represents the first sustained academic scrutiny of Krashen’s framework.

• Gregg, K.R. (1984). Krashen’s monitor and Occam’s razor. Applied Linguistics, 5(2), 79–100.
  Summary: The most cited critique — argues the Monitor Model is theoretically incoherent and empirically unfalsifiable. Initiates the debate that has shaped SLA theory for four decades. Essential for a balanced evaluation of Krashen.

• VanPatten, B., & Williams, J. (Eds.). (2007). Theories in Second Language Acquisition: An Introduction. Lawrence Erlbaum.
  Summary: A comprehensive survey of SLA theories, including the Monitor Model and its successors. Provides context for where Krashen’s framework sits within the broader SLA theoretical landscape and how it has been evaluated, extended, and challenged.

Note:

• The Monitor Model is one of the few SLA theories to have directly and significantly impacted classroom practice, despite being heavily criticized theoretically. The gap between its theoretical influence (contested) and its practical influence (enormous) is a defining feature of Krashen’s legacy.
• The Monitor Model is sometimes confused with the “Monitor Hypothesis” — which is only one of its five components. The Monitor Hypothesis concerns only the role of conscious learning as a self-correction mechanism; the full Monitor Model encompasses all five hypotheses listed above.