Grammar study gets in the way of learning a foreign language. Instead of focusing on common phrases and actual dialogue which is spoken in the language, students are forced instead to memorize conjugation charts and other rules of grammar. The best way to learn a language, as many foreign language teachers would agree, is to travel to the country and live there for a time, wholly immersing oneself in the language on a daily basis. The best resources for learning a language aren't grammar books, but phrasebooks and authentic dialogue. Phrasebooks contain the most commonly used phrases which are used in everyday speech and reading. If we're talking about the basic building blocks of a language, it isn't grammar; it's phrases. Audio dialogue is the next step up, where one listens to a native speaker talking at a normal speed either in-person or through audio books. This is as close as it gets to actually living in the country if one doesn't have the means to do so. As mentioned before, the best way of acquiring a foreign language is to spend a significant amount of time there. Perhaps the best example of this method comes from the movie The Last Samurai, in which the main character is wounded in battle and nursed back to health by a samurai leader. Stuck in Japan with no knowledge of the language whatsoever, he is forced to learn it little by little through his conversations with the samurai who are taking care of him. He becomes fluent in the language in a very short time.
Grammar is the backbone of all languages. Without a firm grasp of the grammar rules of a foreign language, one has no idea how to use the words and phrases which they have acquired. It is one thing to know a list of phrases or to recognize them by ear, but it is another to know how to organize them in a sentence. Otherwise, one is just parroting what they have heard other people say, with no real understanding of what they are saying.
[P1] Knowing grammar isn't necessary to learn a foreign language. [P2] Common phrases are the backbone of any language. [P3] The best way to learn a foreign language is to immerse oneself in it.
Rejecting the premises
[Rejecting P1] Understanding grammar is necessary in learning a foreign language. [Rejecting P2] Grammar is the backbone of any language. [Rejecting P3] The best way to learn a foreign language is to study its grammar and put together phrases in sentences that make sense.