The reason why

Grammarians are divided over the use of why such as in the sentence below:

(1) The reason why he left was unknown.

Specifically, the debate centres on whether why is redundant after the phrase the reason.

Redundancy is the use of unnecessary words or phrases that express something already said in the utterance or sentence. For example, the phrase in colour is redundant in My car is red in colour because red is a colour.

Some grammarians consider the use of why in the expression the reason why redundant and condemn its use. They argue that because both reason and why amount to the same meaning, the word why is unnecessary after the reason. Hence, they advocate the why-less version below:

(2) The reason he left was unknown.

Others argue that the word reason is a noun and does not mean why, a conjunction, and so there is no redundancy. This view is shared by Bryan A. Garner, who pointed out in Garner's Modern American Usage that the phrase the reason why is no more redundant than the time when or the place where.

So, which view do you subscribe to?

I favour the latter view that there is no redundancy in the reason why. Although why can be removed from sentence (1) without any loss in meaning, it does not necessarily follow that its inclusion makes the longer sentence incorrect. In fact, I would even argue that the more verbose the reason why is better than the reason by looking at where since both are conjunctions:

(3) The place where he visited was a tourist spot.
(4) The place he visited was a tourist spot.

Both sentences (3) and (4) are acceptable in English and convey roughly the same meaning. Neither is more correct than the other.

However, consider the next pair:

(5) The restaurant where we ate was horrible.
(6) The restaurant we ate was horrible.

The verbose where version makes the intended meaning of the restaurant as a place where the eating happened unambiguous. The minimalist version, on the other hand, can be misleading. Someone might think we ate the restaurant!

But the expression the reason why must be distinguished from the reason is because. The latter is an outright redundancy, since the word because means for the reason that.