* Past participle: When used as a past participle, it acts as an adjective describing something.
* Example: "The forgotten toy lay in the corner."
* Verb: When used as a verb, it's in the past tense and describes an action.
* Example: "He forgotten his keys." (This is technically incorrect grammar, as the correct past tense of "forget" is "forgot". However, "forgotten" is sometimes used in this way colloquially.)
Therefore, you need to look at the context of the sentence to determine the part of speech.