I guess it is. It all depends how you want to learn. Of course you can learn a language without a single grammar lesson. Billions of people do it every day. Here's how:
1. Spend a year or so sitting on someone's knee, just listening. You don't need to say anything.
2. Get lots of smiles and approval when you say Ga Ga and Goo Goo.
3. Get even more approval when you say Mama or Dada. Do more listening.
4. Start fitting words together, a few at a time. Make a few mistakes, then get it right.
5. After about five years you will speak the language perfectly.
Too long? Haven't got five years full-time, night and day, to learn a language? Want a quick fix? A short cut? Here's one - take some grammar lessons. It's much more efficient, honestly.
Well, we get grammar rules by looking at how we speak and defining the patterns from that. It's reverse engineering. For educated adults, this is very useful because we don't need to spend five years or more babbling words until we sound "perfect". (I'll even say that this point is where we actually start lessons! It'll be another decade or more until a person's language ability starts to reach a high - ie. publishable - standard.)
So let's benefit from the knowledge. :)
By the by... I once did a little bit of online research on the claim "I learnt English without needing grammar". I found two people who openly claimed this. Two. The first one was lying: he was a native speaker who had benefited from a standard education. He certainly learnt grammar at school. The second was a Korean person, if I remember correctly. He could write, but his writing was full of errors.
On the other hand... the first thing I encountered when starting Slovak was its table of declensions. Imagine 3 genders x 4 patterns x 7 cases. Oh, and double that because they have plurals. Then add adjectives, which change accordingly. We hadn't even got to the verbs yet, and any verb needs to be conjugated in 8 ways (I, thou, he, she, it, we, you, they).
It was like being given a bag of chicken bones and told to make a chicken.
Grammar is useful as a reference point, but actually using the language is rather different. We can't ignore grammar (seriously... don't), but we can't make it the be all and end all either.
Great answer,Su.Ki. !
I believe is very important but many seem to ignore it. I found many pages stating that it's not as important and some believe it. (http://www.spokenenglishpractice.com/3-english-speaking-rules-every-non-native-speaker-should-know/#comment-663. I just don't understand how anyone can have a good conversation without knowing the basic rules.
@Peachey- I am gonna check out those pages. :P