Should grammar be taught in L2?

This is part of an answer I provided @Enotes.com 

Should you teach grammar with L2, or just “go with the flow?” That is the question!

The universal consensus is that you should teach any foreign language completely, along with its rules, meanings, proper and ethical usage. The rationale behind this is that language is never taught in isolation. The reason for this is that words and phrases are never used in isolation, either. They come together with reasoning, understanding, and, like you state in your question, explicit, implicit, deductive and inductive meaning.

In order for the human brain to grasp the semantic meaning of a second language, the system itself needs to be “word attacked,” or systematically studied, from the inside out.

While a few English Language specialists may disagree with the way English should be taught, theorists from different generations would support the idea that language should be taught as a system, not as a mere cluster of independent words or phrases.

The Universal Grammar (UG) theory

The UG theory states that grammar consists of a series of processes, principles and categories which are shared by all languages. This theory was initiated in the 13th century, when Roger Bacon proposed that all languages possessed what we can call a grammatical “blueprint,” upon which their systems are built.

Noam Chomsky, one of the most prominent names in linguistics, supports the theory of Universal Grammar and adds,

“Universal grammar is not a grammar, but rather a theory of grammars, a kind of metatheory or schematism for grammar” (Language and Responsibility, 1979).

By “schematism,” Chomsky refers to the way that the language is presented and naturally shows itself along with its form and operative nature.

Another important observation made by Chomsky regarding the importance of grammar and the innate qualities that it carries, is that Universal Grammar does not happen accidentally. Chomsky defines it as

The system of principles, conditions, and rules that are elements or properties of all human languages not merely by accident but by necessity (Reflections on Language, 1975).

Moreover, Stephen Pinker in The Stuff of Thought (2007) speaks about “cracking the language code” in order to learn it best. It all boils down to how children learn languages so quickly.

Just look at how children that speak other languages manage to acquire second language so easily. It is because they directly “attack” the language out of necessity. They are motivated by the prospect of communicating and playing with other kids.

This shows, according to Chomsky’s theory, that we must all be equipped with a set of mechanisms that decode what is known as the “grammar machinery” that accompanies every language.

All this being said, the conclusion is simple: Yes, you must teach grammar. However, your teaching may or may not be primarily responsible for the student’s acquisition of the language. It will be the innate ability of the student to differentiate, use induction, deduction, problem solving, and memory to finally connect all the dots together. Motivation and processing will also be key. The teacher, essentially, is a conduit.