Like - as

In academic English, there is a distinction in the way the two words like and as are used to make comparisons (and the type of comparison called a simile). To use the jargon, like is a preposition, and as is a conjunction. If you are comparing things (nouns, or noun phrases), use like. If you are comparing the way things are done (verbs) you should use as. "She writes as she talks" is correct. "She writes like she talks", though perfectly common in spoken English, is frowned on in academic circles.

In spoken English, the distinction is not maintained. "It's going to be rather cloudy tomorrow, like it was yesterday" said the BBC weather forecast on 12th September 2002, when the rule above would insist on as.

It is also possible to be confused by the 'double' use of as in direct comparisons. "He is as deaf as a post" we say - rather strangely, perhaps; but quite correctly. Here, and in some other contexts, the word as is a preposition. Grammar can be very confusing!

Like can also be used as an adjective. (Here, this is the equivalent of alike, which, with its two syllables, is probably more formal.) It may cause more confusion by being used with as - "She and her sister are as like (adj) as (prep) two peas in a pod"; "He is very like his father."

Overall, the idiomatic use of like and of as, each with its several different meanings and uses, is very hard for non-native students to acquire. Constant reading and practice will make it easier.