Now supposing that this square stands for a, which according to Poe's theory it should, a coming before s in the frequency in which it occurs in ordinary English sentences, how would the phrase look (still according to Poe) with dashes taking the place of the remaining unknown letters?
Thus A-a -- -- if the whole is a single word.
A- a- -- if the whole is a phrase.

That it was a phrase I was convinced, possibly because one clings to so neat a theory as the one which makes the shading, so marked a feature in all the specimens before us, the sign of division into words.

Let us take these seven characters as a phrase then and not as a word.

What follows?
The dashes following the two a's stand for letters, each of which should make a word when joined to a.

What are these letters?
Run over the alphabet and see.