<em>Alternate</em> means every other one, or taking turns: <em>The bins are collected on alternate Tuesdays.</em> <em>Alternative</em> means another option instead of this one: <em>Is there an alternative route to the airport?</em> In American English, <em>alternate</em> is also widely used for the second meaning.
The core difference
Think rhythm versus choice. Alternate describes a pattern that switches back and forth — first this, then that, then this again. Alternative describes a substitute: one thing offered in place of another.
Alternate is also a verb, stressed differently in speech (AL-ter-nate the verb, al-TER-nate the adjective): They alternate between night shifts and days.
How to use each
- alternate (every other): We meet on alternate Wednesdays. / Plant the rows in alternate colours.
- alternate (verb, take turns): She alternates between fury and total calm.
- alternative (other option): We need an alternative supplier. / The alternative is to cancel. / alternative medicine, alternative energy.
The test
Try substituting "every other". If the sentence still means what you intended, alternate is right: every other Tuesday works, so alternate Tuesdays is right. If instead you can substitute "another" or "a different one instead", you want alternative: a different route instead works, so an alternative route is right.
What people actually do
Be aware that the neat split above holds better in British English than American. In the United States, alternate routinely covers the "other option" sense — an alternate route, an alternate ending, alternate history — and American dictionaries record this as standard. It is not an error there.
American English also uses alternate as a noun meaning a stand-in: an alternate juror, she's the alternate on the delegation. British English would say reserve or substitute.
What no dialect does is use alternative for the every-other sense. "Alternative Tuesdays" is wrong everywhere.
The common mistake
The trap is unnoticed ambiguity. We're running alternate services could mean every other service is running, or that a replacement timetable is in place — and passengers will read it both ways. When the stakes are practical, drop both words and write every other or replacement.
A note on "alternatives"
An old rule held that you can only have two alternatives, since the word implied a choice between a pair. Careful writers no longer observe this; three alternatives is standard in every major dictionary. Treat any objection to it as a personal preference rather than a rule of grammar.
Frequently Asked Questions
Is it "alternate route" or "alternative route"?
Both are correct depending on where you are. British English prefers alternative route for a different way round; American English commonly says alternate route and dictionaries there record it as standard.
Can you have more than two alternatives?
Yes. The old rule limiting alternatives to two is no longer observed by careful writers or by dictionaries, so "four alternatives" is fine.
What does "alternate Fridays" mean?
Every other Friday — one on, one off. If you mean a different day instead of Friday, say so explicitly, because readers will assume the every-other sense.