* Conjunction: When it connects two clauses, usually to introduce an alternative.
* Adverb: When it introduces a question or a statement of uncertainty.
Examples:
* Conjunction: "I don't know whether to go to the party or stay home."
* Adverb: "Whether you like it or not, we're going to the movies."
To determine which part of speech "whether" is, look at how it is used in the sentence.