Like vs As

Conjunction 'as' may introduce a clause; the preposition 'like' must be used for a comparison of two nouns.

Use like as a preposition in front of a noun:

He ate like a pig. (like a pig is a prepositional phrase)

Like their data, ours supported the hypothesis. (Like their data is a prepositional phrase)

 

Use the conjunction as, not like, in front of an adverbial phrase or clause:

not We collected data like we did before.

but We collected data as we did before. (as introduces the subordinate clause)

 

not Like we predicted, competition eliminated one species.

but As we predicted, competition eliminated one species. (as introduces the subordinate clause)

 

not It appears like this experiment succeeded.

but It appears as if this experiment succeeded. (as introduces the subordinate clause)

According to Garner, like is adjectival and as is adverbial