On the QWERTY layout of my computer keyboard, the symbol / appears beside the questioning symbol ?. They are represented together on the same key, and I can choose between them by pressing shift. / is the standard function, with ? being the shift-induced alternative. This could be represented as //? although that's slightly confusing. Perhaps if x represents / and y represents ? then we could illustrate the relationship on the key as x/y. This would indicate that the single key allows a choice of x or y (/ or ?) but that both could not be used simultaneously.

For in its truest form / is the mark of the binary. In or Out. On or Off. And or Or.

/ is the mark of bifurcation and mutual exclusivity. It is remarkable in its ability to delineate the state of liminal gulf, as / punctuates the non-space (or dual space) between male/female, up/down, or sun/moon.

/'s other literary function of course is to indicate the line breaks in a piece of poetry if reproduced sans original spacing. Here again it stands for division, marking the distinction of space within otherwise blind prose. The absolute nature of /'s position as punctuation's unequivocal divide is accentuated by its usual spoken name of "The Slash"¹.

The true term for the diagonal line is virgule but, as well as providing a link with Guns N Roses, the designation of Slash suggests an aggression to /'s role of symbolic barrier. Virgule has no such alternate meanings and, indeed, seems to have been made up only to refer to /. "To slash" is a violent act of division that suggests the machete or broadsword. "To slash" is not just "to cut", but also "to wound".

I looked up "slash" in a standard dictionary. In addition to virgule (or as the dictionary affectionately terms it: "a character used to separate optional items in a list or to express fractions or division") I was provided with the following illumination:

slash vt

1. to make long deep cuts in something
2. to cut or attack somebody with the sharp sweeping strokes of a sword, knife, stick, or whip
3. to greatly reduce or shorten something
4. to make a slit in fabric or a garment to reveal the lining
5. to cut bushes and undergrowth from a wooded area

slash n

1. a sharp sweeping stroke of a sword, knife, stick, or whip
2. a long deep cut or wound
3. a slit in fabric or a garment, made to reveal the lining
4. the debris left after trees have been cut down

Under "Meanings" are listed Cut, Gash, and Reduce.
Under "Synonyms" are listed Cut, Hack, Slice, Gash, Slit, Rip, and (my personal favourite) Lacerate.
"Related Terms" include Slash-and-Burn and Slasher Movie.

Significant to my mind is that each of these definitions and synonyms describes the splitting, often in violent terms, of a unified whole. The verb "to slash" seems to indicate the perforation and division of a previously un-perforated object or surface. The noun "a slash" indicates both the gesture that might perpetrate such a gash, and the resulting injury. It might seem peculiar then that / has become known as The Slash, when its usage is typically, as we have seen, to separate already distinctive binary opposites or mutually exclusive states. In this sense / is closer to being an anti-slash; a joining of two opposing whole units through a single clean stitch. The division marked by legions of textual /s is surely not one of a gored and brutalised One, but of a civilised distinction between Two.

The exception of course is that sometimes / does indicate something of a cleaving, albeit is slightly more complex circumstances. Imagine an academic text that describes the movie Frankenstein. In it, the author describes how The Monster/Karloff performs some action or other. Here / is used to both link the actor and the character he plays and to simultaneously distinguish them. The difference between this and the more binary kinds of definition suggested above is that in the Monster/Karloff example the two states (actor/character) are not mutually exclusive. The same text may refer to film/cinema and again the functional distinction would be the same: the position of / indicates to the reader that the two states are related though distinct phenomena that can be discussed together but should nevertheless not be conflated.

There is no spoken equivalent to /. The mark is purely a written one, which is interesting if we think of the relationship between thought and language. Can we conceive a thought that we have no way of conceptually articulating? It's a very old question, but one to which / allows us to posit an addendum. Does it matter if we can only articulate the thought through writing, rather than speaking? What happens if we don't have a pen?

Perhaps after all, /'s attribution is purely a visual one. The classic diagonal mark most closely resembles the central slit in the masked Zorro's iconic signature, which was indeed always produced using a slash of his swashbuckling sword.

¹As well as a Slash, / is also called a Stroke, but that's another story.