s one of the symptoms of fever: if a patient is
not thirsty, you can conclude at once that his illness is not fever,
and the argument, fully expressed, is in the Second Figure.

All fever-stricken patients are thirsty.
This patient is not thirsty.
[.'.] He is not fever-stricken.

Arguments of this type are extremely common.

Armed with the general principle that ill-doers are ill-dreaders,
we argue from a man's being unsuspicious that he is not guilty.
The negative diagnosis of the physician, as when he argues from the
absence of sore throat or the absence of a white speck in the throat
that the case before him is not one of scarlatina or diphtheria,
follows this type: and from its utility in making such arguments
explicit, the Second Figure may be called the Figure of Negative
Diagnosis.

It is to be observed, however, that the character of the argument is
best disclosed when the Major Premiss is expressed by its Converse by
Contraposition. It is really from the absence of a symptom that the
physician concludes; as, for example: "No patient that has not a sore
throat is suffering from scarlatina". And the argument thus expressed
is in the First Figure. Thus the reduction of Baroko to the First
Figure by contraposition of the Middle is vindicated as a really
useful process. The real Middle is a contrapositive term, and the form
corresponds more closely to the reasoning when the argument is put in
the First Figure.

The truth is that if the positive term or sign or necessary condition
is prominent as the basis of the argument, there is considerable risk
of fallacy. Sore throat being one of the symptoms of scarlatina, the
physician is apt on finding this symptom present to jump to a positive
conclusion. This is equivalent technically to drawing a positive
conclusion from premisses of the Second Figure.

All scarlatina patients have sore throat.
This patient has sore throat.

A positive conclusion is technically known as a Non-Sequitur (Doesn't
follow). So with arguments from the presence of a necessary condition
which is only one of many. Given that it is impossible to pass without
working at the subject, or that it is impossible to be a good marksman
without having a steady hand, we are apt to argue that given also the
presence of this condition, a conclusion is implicated. But really the
premisses given are only two affirmatives of the Second Figure.

"It is impossible to pass withou