Reason Why

It is clearly redundant. Many people do many things they ought not to do!

Yes, it's redundant.

But it's not necessarily wrong. It's simply a way of providing more emphasis to the statement. Languages have a tremendous capacity for seemingly redundant constructions.

I should add as an example, "The Reason Why" which is the title of a superb book on the Charge of the Light Brigade by Cecil Woodham-Smith.

If the title were "The Reason" it would lack a certain stylistic quality and emphasis.

I believe your Lordship will agree with me in the Reason, Why our Language is less Refined than those of Italy, Spain, or France - Jonathan Swift, 1712

These observations will show the reason why they poem of Hudibras is almost forgotten - Samual Johnson, 1759

That is one reason why I like reading older novels - Lewis Carroll, 1892

Fear of terrorist attacks is not the only reason why American's are deciding to stay at home - The Economist, 1986

Have you ever asked someone a question, gotten an cursory, insufficient answer, then, after rolling your eyes in exasperation, said something like "duh, I KNOW that. What I want to know is WHY???" I can't think of a specific example right now, but I'm sure the increased specificity of "why" after "reason" in some cases is not redundant, but insures a more relevant answer. Here's a stilted, bad example:

"What's the reason you were late?"
"Because I arrived at 9:15 instead of 9."
"No, you dummy, what's the reason WHY were you late?"
"Ooohhh, um, there was a lot of traffic."

By the way, I know a number of people who will say stuff like that on purpose all the time. Makes you want to smack them upside the head.

Thanks guys. that really helped me. But I hope no one would correct me if I just use one in the sentence, right? for instance, with anonymous' example:
"What's the reason you were late?"

"Because I arrived at 9:15 instead of 9."

I completely see myself asking that question as well. but if I still get the wrong answer, i'd end up asking "No you dummy, what's the reason for you / your being late?" instead of "No, you dummy, what's the reason WHY were you late?"

But that's just me. but given the number of people telling me that it's not wrong as far as semantics are concerned, then I'll stop teaching my students that it's wrong to say it -but i'd still use it. hahahaha
I just found it irritating to listen to. Esp. 1 time when a trainee of my answered me by saying "the REASON WHY it's like that is BECAUSE..." and I was like, ARGH! just pick one! hahaha

Oh, and of course, that should be "...WHY you were ...", not "...WHY were you ...". Oops:)

Joseph, I'll bet you'll find this one irritating too. Surely you've heard: "What it is is..." (sometimes someone will insert a third or even a fourth "is"!!)

Well, it's not redundant, it is a relative clause, and you need to use WHY after REASON to fill grammatically the subordinate clause. You cannot omit it. WHY is acting here as a pronoun, replacing the REASON, and that's why it may sound redundant, but it is not more redundant than other relative clauses with other pronouns, as: 'This is the man who saw the whole thing happen'.
'The man who' is as redundant as 'the reason why' or 'the place where', don't you think so?

No, you can certainly leave it out:

These observations will show the reason they poem of Hudibras is almost forgotten

That is one reason I like reading older novels

Fear of terrorist attacks is not the only reason American's are deciding to stay at home

But there's nothing wrong with "reason why" either.

John, in fact I was so sure because this is what the British Council makes us teach to our students. I'm a Spanish teacher of English and I trust the grammar in books, which is probably wrong or incomplete, sometimes, as your examples show.
I take note, though, of the possibility of leaving it out. Thanks.

When Anonymous says:

"Makes you want to smack them upside the head."

What side is the upside? Is it the top? As in upside down? Or is the phrase a contraction of:

"Makes you want to smack them up the side of the head."

As in a swift uppercut blow to the side of the head. (Quite violent when you think about it).

It's perhaps redundant, but not necessarily so.

But it's correct. What's incorrect is to say "the reason why is because..."

Is there a reason why every example of leaving out one part of the phrase "the reason why" chooses to leave out why instead of reason?

That is the reason why I like reading novels.
That is the reason I like reading novels.
That is why I like reading novels.

All three usages seem to have the same meaning, yet every example so far of dropping one portion has dropped the why rather than the reason.

Is it possible that the "reason why" has become verbal/written shorthand for "reasoning why"?

I've learned a lot from all the comments and have come to the conclusion that the usage is circumstantial, i.e., depends on the attendant conditions. This morning I heard a dignified-sounding talker on the radio say, "It depends on where you're at." This construction always rankles me in the same way as does "the reason why" or, more so, Anonymous's "what it is is..." Now, however, I am swayed by John's quotations from classical writers and have decided that the "why" is indeed an emphatic in some situations and is detritus in most other situations.

Well at least it's a good song:

http://www.youtube.com/watch?v=xuQvja_t1FY&feature=related

All of John's examples which leave out why sound very wrong to me. I would always include why or some other word, for the reason that Lourdes pointed out.

The verbose example given above is unsatisfactory in numerous respects:

"What's the reason you were late?"

"Because I arrived at 9:15 instead of 9."

"No, you dummy, what's the reason WHY were you late?"

"Ooohhh, um, there was a lot of traffic."

When the question is rephrased, the words "what's the reason" become superfluous. The rephrased question should be just "No, you dummy, WHY were you late?"

Leaving that aside, the questions are functionally identical, and the answer should have been the same. The response to the initial question ("Because I arrived at 9:15 instead of 9") is not a proper response. The respondent merely indicates that he/she was late, but that's not what the questioner was asking. The question itself indicates that the person was late, and the questioner wants to know why the person was late. The rephrased question asks the same thing, but in this case the respondent gives a proper response.

The phrase 'the reason why', as pointed out, has a long history but is it correct? I would say "the reason that I am late..." or "the reason for my lateness..."
"The cancellation of the train is the reason that I am late."
But I accept that 'the reason why' is a hardy indefensible that isn't going away.