Dictum de omni
An editor has nominated this article for deletion. You are welcome to participate in the deletion discussion, which will decide whether or not to retain it. |
In Aristotelean logic dictum de omni (sometimes misinterpreted as universal instantiation) is the principle warranting an inference from a truth about a kind of thing to the truth about a subkind of that kind. It is thought to be one of two ultimately basic principles (along with dictum de nullo, below) in syllogistic logic in the sense that all syllogistic argument forms are variations of applications of these two principles.
Example:
(1) Dogs are mammals.
(2) Mammals have livers.
Therefore (3) dogs have livers.
Premise (1) states that "dog" is a subkind of the kind "mammal".
Premise (2) is a (universal affirmative) claim about the kind "mammal".
Conclusion (3) states that what is true of the kind is true of the subkind.
Dictum de nullo is the related principle that whatever is denied of a kind is likewise denied of any subkind of that kind.
Example:
(1) Dogs are mammals.
(4) Mammals do not have gills.
Therefore (5) dogs do not have gills.
Premise (1) states that "dog" is a subkind of the kind "mammal".
Premise (4) is a (universal negative) claim about the kind "mammal".
Conclusion (5) states that what is denied of the kind is denied of the subkind.
Related Topics
Syllogism
Class (philosophy)
Class (set theory)
Natural kind
Type
References
Prior Analytics, 24b, 28-30.
External Links
Logical Form (Stanford Encyclopedia of Philosophy)