One teacher said, "Tom did his homework like a good boy should." Another teacher said that this is wrong and it should be, "Tom did his homework as a good boy should." Who is correct?
The first teacher argues that English speakers normally use the word like as a conjunction (and, or, but...) meaning similar.
The second teacher argues that the word like is a preposition (under, over, in, on) also meaning similar. This teacher claims that the conjunction as should be used instead of the word like.
like used as a conjunction (similar to): His flat smells like it was a garbage dump.
like used as a preposition (similar to): It looks like good weather.
as used as a conjunction (similar to): That ship's bread is as hard as a rock.
I tested these sentences on some native-speaking English teachers. They couldn't see the difference.How can we expect Chinese-first language students to understand it? The hint is that if as, as if or such as can be correctly substituted for like then it is being used as a conjunction.
In English a usage is more acceptable if it is older and more common. The argument about using the word like as a conjunction is recent. The word like has long been used as a conjunction in formal English for about six hundred years. It has only been since the 19th century that troublesome reforming teachers created the rule that the word like cannot be a conjunction. Most native speakers have ignored them and kept speaking as they have for centuries.
My Longman and Oxford dictionaries both accept the word like as a conjunction meaning “in the same way as”. The recent objection to the word like as a conjunction is groundless. Both also say that it is informal and note that there is a disagreement. (So it is not an unqualified endorsement. There is no harm in avoiding the conjunctive use on an English test.) The word like is one word, with one meaning, that is both a conjunction and a preposition. If you have trouble telling the difference, don't worry about it. Outside of the classroom, real English uses the word like both ways.
However the disagreements over the word like do not end here. It has many functions in English and cannot be learned as a normal word. These other uses will be covered in next week's article.