As or Like

While as and as if are conjunctions, like is a preposition: As you know, It’s as if you were lying, You look like a clown. A causal as that appears mid-sentence can be confused to mean while and should thus be avoided.

Traditionally, like functions as an adjective, modifying nouns or pronouns, not as an adverb. Although like often replaces as and as if in colloquial use, proper usage requires like to function as a preposition (and the object of a prepositional clauses takes the objective case): He likes us, We are like them.