What does each mean when used as the first word in a statement/sentence? Is the emphasis the same or does one indicate more forcefulness/certainty than the other? Is surely suitable below or does it imply a question? Are both equal to an exclamation mark(!) ?
e.g. Indeed/Surely, to those who disbelieve, a nod is as good as a wink to a blind horse.
Indeed is used when the statement that follows is reaffirming or reinforcing a point that was made earlier.
Surely can have that meaning, but it also frequently implies contradiction or disbelief: "Surely this can't be what he meant." (Note that "Surely", like "obviously", frequently means that the statement which follows is not actually certain or obvious--only that the speaker wishes it were!)
Either of these words might be appropriate in your example sentence, but it would depend on the context. The idiomatic expression "A nod is as good as a wink to a blind horse" means that a small hint will be enough to communicate the intended meaning.
If the previous sentence were:
James' single raised eyebrow said everything.
I would think "Indeed" would make more sense.
If the previous sentence were:
It's not always necessary to spell everything out explicitly.
Then I would think "Surely" would be a more appropriate beginning for the sentence.
Both could be followed by an exclamation point, or could not; again, it depends on the context. Neither one would necessarily communicate the meaning of the exclamation point without the punctuation itself.
