figure, that the premisses must be of opposite quality; the one must affirm and the other deny. Therefore here the principal rule is: Sit altera negans; the corollary of which is: E meris affirmativis nihil sequiter; a rule which is sometimes transgressed in a loose argument obscured by many parenthetical propositions. The course of thought which this figure exhibits distinctly appears from what has been said. It is the investigation of two kinds of things with the view of distinguishing them, thus of establishing that they are not of the same species; which is here decided by showing that a certain property is essential to the one kind, which the other lacks. That this course of thought assumes the second figure of its own accord, and expresses itself clearly only in it, will be shown by an example:
All fishes have cold blood;
No whale has cold blood:
Thus no whale is a fish.
In the first figure, on the other hand, this thought exhibits itself in a weak, forced, and ultimately patched-up form:
Nothing that has cold blood is a whale;
All fishes have cold blood:
Thus no fish is a whale,
And consequently no whale is a fish.
Take also an example with an affirmative minor:
No Mohamedan is a Jew;
Some Turks are Jews:
Therefore some Turks are not Mohamedans.
As the guiding principle for this figure I therefore give, for the mood with the negative minor: Cui repugnat nota, etiam repugnat notatum; and for the mood with the affirmative minor: Notato repugnat id cui nota repugnat." Translated these may be thus combined: Two subjects which stand in opposite relations to one predicate have a negative relation to each other.
The third case is that in which we place two judgments
