When do you put a comma before "as"?

When was the last time you memorized a punctuation rule before a conjunction? Anyway, here's the basic rule: you put a comma if "as" introduces a comparative clause or an adjoining sentence. For example: "She sang like a bird" or "He made noise as always." A comma is necessary here! But if "as" is part of the conjunction "because" (the reason), then the comma is already governed by where that conjunction appears in the sentence.

There are moments when you DON'T put a comma. If "as" means "in the capacity of" - no comma at all! "He works as a teacher," "This will come in handy as a backup option." Another case - phraseological expressions and set phrases like "works like clockwork" or "happy as a lark," though linguists disagree on this one, and many still put a comma to be safe.

The simplest way to check yourself: if you can mentally insert the words "just like" or "at the same time as" before "as," then a comma is needed! If it's about a role or function (as = in the capacity of), then there's no comma. With time this will start working automatically!