Took is the simple past tense and stands on its own: "I took the train." Taken is the past participle and cannot stand alone — it needs a helper verb such as have, has, had, or a form of be: "I have taken the train", "the train was taken". If there is no helper verb in the sentence, you want took.
The core difference
Both are past forms of take, but they are not interchangeable. Took is the simple past — a complete action, no helper needed. Taken is the past participle, which is grammatically incapable of standing alone as the main verb.
The helper-verb test
Look for a helper verb (have, has, had, was, were, been, being). If one is there, use taken:
- took — no helper: She took my advice.
- taken — with have/has/had: She has taken my advice.
- taken — with be, forming the passive: My advice was taken.
The mistake people actually make
The common error runs in one direction: "I have took it" instead of "I have taken it". It is frequent in speech in many English dialects, and it is the form to watch for in writing. The reverse error, "I taken it" without a helper, is rarer but equally non-standard.
A quick check
Swap in saw and seen, which follow exactly the same pattern and where most people's ear is reliable. If "I have saw it" sounds wrong, then "I have took it" is wrong in the same way — and the fix is the same.
