A Relation of Ideas, in the Humean sense, is the type of knowledge that can be characterized as arising out of pure conceptual thought and logical operations (in contrast to a Matter of Fact). In a Kantian philosophy, it is equivalent to the analytic a priori. It is also closely coincident with the so-called Truths of Reason of Leibniz, which are defined as those statements whose denials are self-contradictory.

Examples:
Mathematics: 8 x 10 = 80.
Logic/Definitions: All islands are surrounded by water (by definition).

How We Know:
-We can demonstrate these truths.
-Denying these will lead to a logical contradiction.

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