When I was first learning about the research on second language acquisition and was trying to figure out what it meant to teach using comprehensible input, one of the biggest obstacles for me was understanding the role of explicit knowledge. “Explicit knowledge” refers to being able to state a fact or a “rule” about a feature of language. For example, if a person has explicit knowledge about the future tense in English, they would be able to say something like, “We use will or be going to before a verb to indicate that something will happen in the future.”

It definitely seems like explicit knowledge helps a person learn a language. If you teach students about a particular grammar rule, they can usually understand the rule and apply it in controlled practice activities. And explicitly learning about a grammar rule can help students to understand the language they hear.

But people don’t need to have explicit knowledge in order to speak a language. For example, most people don’t know much about the grammar rules of their native language, but they are fully capable of speaking it. And the concept is true for second language learners, too. Many people are able to acquire a second language without learning about grammar rules. And even those who do learn some grammar rules don’t learn everything there is to know about the grammar of that language—but if they have received enough input, they can produce correct forms without explicitly learning about them. In other words, they have implicit knowledge, not explicit knowledge.

So then, what is the role of explicit knowledge?

For me, the best way to understand it is through Bill VanPatten’s metaphor of a “crutch,” which he mentions in his book From Input to Output. He writes:

“Imagine a person with a broken leg who uses crutches. The crutches not only help the person walk, they also help to keep the leg immobile. Immobility is required (along with calcium and other things) for the broken bone to heal. When the leg is healed, we do not say that the crutches caused the healing nor that the crutches turned into the person’s leg. We say the crutches facilitated the processes used in healing. In SLA, explicit knowledge may be used as a ‘crutch’ under certain conditions while the processes used to develop a rule in the implicit system have their chance to work” (p. 58).

Explicit knowledge is a “crutch” that can temporarily help learners to express something that is beyond their current ability level. People acquire language by receiving comprehensible input (by listening to and reading language that they understand). But it takes a long time to get enough input to become proficient in the language, so in the meantime, learners can sometimes rely on the “crutch” of explicit knowledge to get by when they need to produce language that they haven’t yet acquired.

VanPatten also briefly mentioned this idea in Tea with BVP episode #47, when he said that explicit knowledge allows learners to “fake” a higher level of proficiency than they actually have.

I like the metaphor of a crutch because it accurately portrays the two sides of explicit knowledge: On the one hand, it can be helpful as a short-term fix. However, it also has severe limitations. As Stephen Krashen argues in his Monitor Hypothesis, learners can only use their explicit knowledge when three conditions are met: 1) They have time to think about and apply the rule, 2) They are focusing on form, and 3) They know and remember the rule that applies in that situation. In real-life communicative situations, these three conditions are rarely met.

A teacher who spends most of the class time teaching students about grammar rules, doing grammar drills, or quizzing students on the definitions of vocabulary words is like a doctor who treats a patient with a broken leg by giving the patient many pairs of crutches but doesn’t actually do anything to heal the broken leg.

Explicit knowledge about grammar can be helpful at times, but it definitely shouldn’t be the focus. Explicit knowledge is a temporary crutch, but comprehensible input is what students really need if they are going to succeed in the long term and if they want to actually be able to use the language in communicative situations (and not just fill in the blanks on a worksheet).

In my classroom, I don’t give long grammar explanations, and I don’t do grammar “practice activities.” I do give occasional grammar “pop-up” lessons (an idea from TPRS). “Pop-up” lessons are extremely short (usually less than 30 seconds), and they give a brief explanation of a grammatical feature. For example, if I say the sentence “She went shopping yesterday,” and if this is the first time students are encountering the word “went,” I would quickly explain: “The word ‘went’ is like ‘go,’ but it’s in the past. In English, we need to change the verb when we talk about the past.”

This explanation helps students to understand both the meaning of “went” and why I used “went” instead of “go”—without having to spend lots of class time explaining complicated grammar rules or drilling students. Furthermore, these pop-up lessons only occur in meaningful contexts. I give the explanation to help the students understand the language they just heard—not “because we’re doing unit 7 in the textbook, and unit 7 teaches the past tense.”

VanPatten also points out in From Input to Output that there is debate among SLA researchers about what exactly the role of explicit knowledge is and to what extent it is helpful to learners. Some researchers believe that explicit knowledge can play a fairly important role, and some researchers believe that it plays almost no role. However, despite these differences in opinion, there is a strong consensus among SLA researchers that input is the essential ingredient for acquiring a language—not explicit knowledge.

Thinking of explicit knowledge as a crutch has helped me to understand how it can be used effectively in the classroom while also reminding me of its limitations. For me, the focus of every class is always the same: to give students lots and lots of comprehensible input.