Handbook of the History of Logic: - Fordham University Faculty

The Assimilation of Aristotelian and Arabic Logic up to the Later Thirteenth Century 333
Socrates is a human being
Therefore: Socrates is an animal
It can be made into a syllogism by adding the major premise: “Every human being
is an animal”. An enthymem can always be reduced to a syllogism by adding or
making explicit the missing premise. An argument by example is based on the
similarity between things expressed by the terms. The argument:
It is not good to drink too much wine
Therefore: It is not good to drink too much whiskey
This is a valid argument because wine and whiskey are both alcoholic beverages.
An argument is confirmed by a locus, which is defined in the following way:
A locus settles an argument or it draws out the argument from the
proposed question.
A locus is hence what makes something into an argument.
The loci are divided into maximal loci and maximal different loci. The first
is identical to the maximal propositions. They are the most prior propositions
and the best known, since given the terms included in them they are necessarily
true. Peter gives the following examples: “Every whole is greater than its
parts”, “Whatever the definition is predicated of, the defined thing is as well”,
and “Whatever a species is predicated of, its genus is as well”.
The maximal different loci are that by which one maximal proposition differ
from another. In the examples: ‘whatever a definition is predicated of the thing
defined is as well’ and ‘whatever a species is predicated of, the genus is as well’,
the components that differ in these are ‘definition’, ‘defined’, ‘species’, and ‘genus’.
These terms are the maximal different loci. These are further divided into intrinsic,
extrinsic, and middle.
The intrinsic loci are the ones involving arguments that are substantive of a
thing, like a definition. The extrinsic loci are the ones involving arguments completely
separated from a thing’s essence, like arguments from opposites. The example
Peter gives is if we question whether Socrates is white and conclude that
‘Socrates is black, hence he is not white’. The maximal proposition in this case
is: ‘If one contrary is posited, then the other is excluded’. A middle locus is taken
from things partly agreeing with the terms posited and partly differing. An example
would be querying whether justice is good and concluding that ‘a just thing is
a good thing, hence justice is good’. The maximal proposition is ‘what inheres is
one conjugate is in the other thing as well’. The discussion of the division of loci
is ended by a list of loci and maximal propositions, which does not differ from the
list Boethius gives in De differentiis topicis.
This is Peter’s list of different loci:
I. Intrinsic loci from the substance of a thing: