Why does the adjective "few" change the plurality of the noun it modifies? [duplicate]

Solution 1:

"I have a few friends" is just the same as saying "I have some friends".

"I have few friends", however, implies that you have only a few friends (as opposed to many). In some contexts (not always!), it can also imply that you don't feel very well about it, that you wish you had more friends.

Also, note that there is a very common expression "quite a few", which is a trap for foreign learners because it looks like it should mean "rather few, very few" — but it does not. It means the exact opposite thing: "a large or significant number, many". So, saying "I have quite a few friends" is the same as saying "I have quite a lot of friends".

Let's have a look at two more examples:

• "A few people think that smoking is healthy."
  = Some people think that smoking is healthy.

  "Few people think that smoking is healthy."
  = Only a few people, a very small number, think that smoking is healthy; most think that it is not.

  "Quite a few people think that smoking is healthy."
  = Many people, a (surprisingly) large number, think that smoking is healthy.

• "This car comes in a few colors."
  = This vehicle model is available in several colors, a number/selection of colors, but less than many.

  "This car comes in few colors."
  = This model is available in only a few colors, just a few colors; less than a few. The speaker probably wishes there were more to choose from.

  "This car comes in quite a few colors."
  = This model is available in more colors than you might think; quite a bunch/variety/selection/gamut of; rather many; the speaker didn't really expect to have such a choice, or thinks you are unlikely to expect it.

Solution 2:

few = not very many, with a focus on the fact that this number is (remarkably) small.

"a few" = not very many, but at least more than one.

Your examples (1) and (2) are talking about the same number of friends, but (1) focuses on the fact that this is a small number and carries a negative connotation, like you don't have as many as one should/could have.

You can also have this apply to something that it is bad to have a lot of and reverse the connotations:

1. I have few enemies. (it is somewhat noteworthy how small the number is; good connotation)
2. I have a few enemies. (I don't have a large number of enemies, but I have more than one)