the case of Singular propositions, the distinction is not
needed and does not apply. Put the question "Is Socrates wise?" or
"Is this paper white?" and the answer "No" admits of only one
interpretation, provided the terms remain the same. Socrates may
become foolish, or this paper may hereafter be coloured differently,
but in either case the subject term is not the same about which the
question was asked. Contrary opposition belongs only to general terms
taken universally as subjects. Concerning individual subjects an
attribute must be either affirmed or denied simply: there is no middle
course. Such a proposition as "Socrates is sometimes not wise," is
not a true Singular proposition, though it has a Singular term as
grammatical subject. Logically, it is a Particular proposition, of
which the subject-term is the actions or judgments of Socrates.[2]

Opposition, in the ordinary sense, is the opposition of incompatible
propositions, and it was with this only that Aristotle concerned
himself. But from an early period in the history of Logic, the word
was extended to cover mere differences in Quantity and Quality
among the four forms A E I O, which differences have been named
and exhibited symmetrically in a diagram known as: The Square of
Opposition.

A______Contraries______E
|\ /|
| \ s |
| C e |
| o i |
| n r |
| t o |
S r t S
u a c u
b \ i b
a \ d a
l \/ l
t /\ t
e / d e
r / i r
n a c n
s r t s
| t o |
| n r |
| o i |
| C e |
| / s |
|/ \|
I____Sub-contraries____O

The four forms being placed at the four corners of the Square, and
the sides and diagonals representing relations between them thus
separated, a very pretty and symmetrical doctrine is the result.

_Contradictories_, A and O, E and I, differ both in Quantity and in
Quality.

_Contraries_, A and E, differ in Quality but not in Quantity, and are
both Universal.

_Sub-contraries_, I and O, differ in Quality but not in Quantity, and
are both Particular.

_Subalterns_, A and I, E and O, differ in Quantity but not in Qua