whether

Whether is a conjunction used to introduce alternatives or indirect questions. It comes from Old English hwæþer, meaning "which of two," and has long served to mark doubt, choice, or inquiry in English.

The primary uses are twofold. First, whether introduces indirect questions after verbs such as know, wonder, ask, decide, or doubt: "I wonder whether she will come." Second, it marks alternatives or decisions, often in the construction "whether ... or not" or in phrases such as "whether to go" or "whether to stay." Examples: "We are unsure whether to proceed," "Please tell me whether you can attend."

In contrast to if, whether is used to present two or more possibilities rather than to express a condition. After many verbs of reporting or thinking, whether is preferred in formal style: "He asked whether the plan would work." In informal speech, if can occasionally replace whether, but not in all cases: "I don't know if/ whether he will come"—the choice can subtly shift emphasis.

Other uses include embedding a clause after a preposition and forming noun phrases such as "the question whether we should invest" or "the doubt about whether they would sign." Grammatically, when the clause is finite, the subject follows whether (whether he comes); with an infinitive, it takes "to" (whether to go).

Etymology notes: from Old English hwæþer; cognate with related forms in Germanic languages. The term remains a staple in formal and written English for expressing alternatives, doubt, or indirect inquiry.