Like vs. As if

Like is a preposition and as if is a conjunction and they state something that is not true, but it is like something true and compare a real situation with an imaginary situation. They both follow verbs such as seem, sound, look, act, behave…

When using the two, note that like is directly followed by a noun or an object and as if followed by a clause:

- It looks like it will rain. (Incorrect)

- It looks like rain. (Correct)

- It looks as if it will rain.(correct)

- He behaved them as if his children. (Incorrect)

- He behaved them as if they were his children. (Correct)

- He behaved them like his children.(correct)

Now compare the following sentences:

- It looks like it’s going to rain.

- It looks as if it’s going to rain.

Strictly speaking, Only the second sentence is right because like here is used to introduce verb phrases while it is a preposition and comes with nouns; but it is unlikely you don’t hear the first context in conversations.

Other examples:

- It seems /sounds/ looks like good (incorrect)

- It seems to be a good idea/seems /sounds/ looks like a good idea (correct)

- It seems /sounds/ looks as if it were a good idea.(correct)

As vs. As if vs. Like

Note the following sentences:

1- He acts as a teacher.(his job is teacher)

2- He acts as if he is a teacher.

3- He acts like a teacher.

 2&3 mean he is not a teacher but acts in a way that he seems to be a teacher