Comparison is the process of establishing whether or not two individuals, two situations, two systems… present or not some similarities or analogies. A process of comparison is involved in many argumentative activities, such that the label argument by comparison (a comparatione) is used with different meanings.
These meanings primarily correspond with the argument a fortiori, the arguments a pari, by analogy, by example or exemplum.

Comparison and categorization — Comparison is the basis for the categorization-nomination process; the individual to categorize is compared either with a known individual belonging to the category, or with the prototypical member defining the category. S. Justice

Intra-categorical comparison — Two beings belonging to the same category are identical from the point of view of this category. Despite this, they can still be compared in terms of:

— their non-categorical properties; S. Intra-categorical analogy.

— their position relative to a prototypical subcategory of this category. A rat and a whale, for example, are identical insofar as both are mammals; considering that the cow is a prototypical mammal, we can say that a rat, being nearer to a cow than to a whale, is “more” a mammal than a whale.

— Hierarchized categories contain by definition built-in comparisons: Bachelor, Master, and Doctorate are three kinds of academic degrees, listed by ascending order. They can enter in an a fortiori argument.

Comparison and structural analogy — A process of comparison is also involved in establishing a structural analogy.