An expression or exclamation that something is exceedingly obvious or apparent, or that one would have to be extremely foolish not to realize something immediately.
An exclamation used to express pleasant or unpleasant mild surprise, indignation, or impatience.
Reason.
For which cause, reason, or purpose.
The cause, reason, or purpose for which.
Introducing a noun or other phrase.
Introducing a verb phrase (bare infinitive clause).
Introducing a complete question.
With a negative, used rhetorically to make a suggestion.