Functions and notions

Similarity

Like and as

Like and as are both be used to say that things are similar. Like is a preposition, and is followed by a noun or a pronoun.

• She sings like a bird.
• You write like me, with your left hand.

We often use like after verbs of the senses (look, sound, feel, taste and smell).

• This smells like leather, but it doesn't look like it or feel like it.
• What are the neighbours cooking? It smells like curry.
• You sound like your mother when you get angry.

As is a conjunction, and is followed by a subject + verb or by a prepositional phrase.

• Nobody sings as I do.
• In summer, as in winter, we go to the mountains.

In informal speech, like is often used as a conjunction.

• Nobody sings like I do.
• Like I said, I don't enjoy this.

As
Other uses of as are the following: 

• She works as an electrician. (preposition)
• You'll be as tall as your father. (adverb) 
• As it was getting late, I went to bed. (conjunction, meaning because)
• It started to rain as we left the building. (conjunction, meaning while)
• Late as we were, they still let us in. (conjunction, meaning although)

Like
Other uses of like are the following: 

• He looks like his mother. (preposition, meaning similar to)
• We threw a few prawns on the barbecue, like they do in Australia. (conjunction, meaning similar to)
• It's not like you to be lost for words. (preposition, meaning typical of)
• I prefer colours like blue or grey. (preposition, meaning such as)
• I was, like, so angry when I heard what he had done. (adverb, expressing attitude/feeling)
• He's, like, really helpful. (adverb, expressing a pause)
• The exhibition is housed inside a low-lit cathedral-like space. (suffix)

(Not) as + adjective / adverb + as

We use (not) as + adjective / adverb + as to say that two things are equal.

• Her new film's just as good as her last one.
• I can't type as quickly as Jan.

(Not) as much / many + noun + as

We use (not) as much / many + noun + as to say that two quantities are equal. We use as much with uncountable nouns and as many with countable nouns.

• He earns as much money as a company director.
• The party was good, but there weren't as many people there as we expected.

Similar to, identical to, the same as

We use similar to express the notion of similarity. We use identical to and the same as to say that there is no difference between two things.

• This article is similar to one I read on the Internet recently.
• This watch is identical to / the same as a real Rolex.

For information about other comparative forms, see Functions and notions, Comparison.