I will use an X to indicate that a box is definitely empty; and an O to indicate that it is definitely full.
Welton's diagrams are similar, but they are along a line:
| S P | S-P |-S P |-S-P |
(I have rearranged Welton's cells so that the similarities to the biliteral diagrams are more obvious.) Welton proposed an unbroken line to indicate presence, a blank to indicate absence, and a broken line when the matter is undecided. I'll use Os and Xs again instead, just because it is easier.
Tom's types are then diagrammed in the following ways:
| X | | | |
| | X | | |
| | | X | |
| | | | X |
| O | | | |
| | O | | |
| | | O | |
| | | | O |
From this the character of the eight types is visible.
Tom suggests that the following holds true:
-[-S+P] = (+S-P)
-[-S-P] = (+S+P)
-[+S-P] = (-S+P)
-[+S+P] = (-S-P)
It can easily be seen from the diagrams that he's right. To negate [ ] you switch out your X's for O's; to negate ( ) you switch out your O's for X's.
More can be said on this; and I'll probably say a bit more in a future post (I don't know when it will come out) on using Welton diagrams for propositional logic.