There’s nothing more embarrassing then correcting someone’s language only to realize that your correction contains its own error. Like maybe the one in our first sentence. Did you see it? That harmless little four-letter word then. It should have been than.
People get tripped up on then and than all the time—and why not? They look and sound so similar, and both words function as linguistic workhorses—then is most often an adverb, while than is usually a conjunction—which means that we mostly use them to connect more obviously significant nouns, verbs, and adjectives.
The way to keep the pair straight is to focus on this basic difference: than is used when you’re talking about comparisons; then is used when you’re talking about something relating to time.
Than is the word to choose in phrases like smaller than, smoother than, and further than. And it’s the word that follows other, rather, less, and more.
Then—the option to choose when time is involved—fits in the phrases just then and back then, and after words like since and until. It’s also in the phrases and then some, every now and then, and even then.