You know what’s a lost art? Starting a sentence with “Why.” It’s so antique, in fact, that I can’t articulate when you’re allowed to do it.
I understand that the initial “Why” can denote mild surprise:
Why, I had no idea you were from Boonestown!
or some kind of vague intensification:
Why, you dirty rat
or can function something like intial “Well”:
Why, it’s quite simple, Maxine….
or can even serve as a phonetic wind-up:
Why, I oughtta…
But you clearly can’t put “Why” before any old declarative sentence: my idiolect rejects “Why, I’ll have the eggs benedict and a coffee.”
Can anyone put their finger on the underlying rule here?
Quomodocumque 
It’s kind of a funny usage. It’s a little like the word “well” in sentences like “Well, it’s like I was saying…” It’s not entirely clear what the “well” is doing there. (And that one, strangely enough, translates almost literally into French: “Eh bien, c’est comme je disais…”)
Why not?
I agree that the sentence you wrote sounds odd. But if you write out the contraction “I will”, then it sounds fine to my ear: “Why, I will have the eggs Benedict and a coffee.”
To one’s self: “What should I have for breakfast today? Is there anything that would really get this day off on the right foot, rev my engines, put a spring in my step? Why, I’ll have the eggs benedict and a coffee!”
Why, you’re absolutely right! (First usage above.) So why is Graham’s sentence OK and mine is not? Note also that Graham’s sentence wouldn’t work with “Well.”
I think here it’s akin to the first usage, indicating mild surprise/discovery/realization.
Why you little!…… aaaaaackkkkhh
My own idiolect doesn’t reject “Why, I’ll have the eggs benedict and a coffee.” I suppose context has a lot to do with it. It does seem a little strange, and your partners at the table would raise an eyebrow: it’s like you’re indicating some power or profundity in “I’ll have the eggs benedict and a coffee” which isn’t appropriate. Graham nicely illustrates a context where it’s not just technically grammatically correct, but also appropriate.
[…] correct way of starting a sentence with why instead, like Jordan S. Ellenberg writes about here: I understand that the initial “Why” can denote mild […]
I vaguely suspect that it may bear some resemblance to our Spanish-speaking cousins (whom themselves may have derived it from Latin), wherein “porque” means both “why” (as in the question) as well as “because.”
What about “Why be sorry when you can be safe” – is this a question or a sentence?
My oldest neighbor jack used this extensively. He was in his eighties in the eighties. It was always at the beginning of any sentence he wished to really drive home to you. “Why, modern Rock and roll music is the wail of China, and the lament of India, against the drums of Africa!” Was one classic from him. Typically he was in a introspective mood when it was used. Something he felt strongly about because of prior meditation or experience.
Thanks for sharing this!
I’ve noticed my son staring random sentences with “why” and feel like he sounds very old fashioned. I always thought he’s got an old soul! Lol