How vs. Why — What's the Difference?

In what manner or way; by what means

For what reason or purpose

In what state or condition

(with reference to a reason) on account of which; for which

To what extent, amount, or degree

Expressing surprise or indignation

For what reason or purpose; why

Used to add emphasis to a response

With what meaning

A reason or explanation

By what name

For what purpose, reason, or cause; with what intention, justification, or motive

By what measure; in what units

The reason, cause, or purpose for which

What. Usually used in requesting that something be said again

Usage Problem On account of which; for which.

Used as an intensive

The cause or intention underlying a given action or situation

The manner or way in which

A difficult problem or question.

That

Used to express mild surprise, indignation, or impatience.

In whatever way or manner; however

(interrogative) For what cause, reason, or purpose.

A manner or method of doing something

Introducing a complete question.

To what degree or extent.

Introducing a verb phrase (bare infinitive clause).

In what manner:

Introducing a noun or other phrase.

By what means.

(relative) For which cause, reason, or purpose.

With overtones of for what reason.}}

(fused relative) The cause, reason, or purpose for which.

In what form, shape, measure, quantity, etc.

Reason.

With what meaning or effect.

An exclamation used to express pleasant or unpleasant mild surprise, indignation, or impatience.

By what title or what name.

For what cause, reason, or purpose; on what account; wherefore; - used interrogatively. See the Note under What, pron., 1.

At what price, for what amount (of money).

For which; on account of which; - used relatively.

In what state or condition.

The reason or cause for which; that on account of which; on what account; as, I know not why he left town so suddenly; - used as a compound relative.

Used as a modifier to indicate surprise, delight, or other strong feelings in an exclamation.

A young heifer.

The manner or way in which.

The cause or intention underlying an action or situation, especially in the phrase `the whys and wherefores'

In any way in which; in whatever way; however.

Question word; what is the reason (`how come' is a nonstandard variant);

That, the fact that.

The means by which something is accomplished.

(dialectal) An artificial barrow or tumulus.

(dialectal) A small hill in northern England. (Usage preserved mainly in place names.)

A greeting, used in representations of Native American speech.

In what manner or way; by what means or process.

To what degree or extent, number or amount; in what proportion; by what measure or quality.

For what reason; from what cause.

In what state, condition, or plight.

By what name, designation, or title.

At what price; how dear.

To what extent or amount or degree;

In what way or manner or by what means (`however' is sometimes used as an intensive form of `how');