Using As and Like When Comparing

As or like?

As and like are prepositions or conjunctions. The prepositions as and like have different meanings. As + noun means ‘in the role of’, like + noun means ‘similar to’ or ‘in the same way as’.

Compare

1. As your father, I’ll help you as much as I can.

The speaker is the listener’s father.

2. Like your father, I’ll help you as much as I can.

The speaker is not the father but wishes to act in a similar way to the father.

We use like (but not as) to compare two things:

She’s got a headache like me.

Not: She’s got a headache as me.

Like the other students, he finds it a bit difficult to get to lectures early in the morning.

Not: As the other students, he finds it …

When we compare appearance or behavior, we use like, not as:

That house looks like a castle.

Not: That house looks as a castle.

As is commonly used to talk about jobs:

He worked for a long time as a teacher in Africa.

Not: … like a teacher in Africa.

The conjunctions as and like have the same meaning when used in comparisons. Like is a little more informal.

Nobody understands him as I do.

Nobody understands him like I do.

from English Grammar Today