Ignotum per ignotius refers to an explanation more unfamiliar than the concept which it seeks to explain.

An example would be: "The oven felt hot because of Fourier's Law." It is unlikely that a person unfamiliar with the hotness of ovens would be illuminated by a reference to the fundamental laws of physics. Of course, such a person might exist in theory, so ignotum per ignotius is not strictly a logical fallacy; it is just a criticism of an argument on rhetorical grounds, stating that such an argument is not useful in a particular context.

Ignotum per æque ignotum

Ignotum per æque ignotum, meaning "the unknown by the equally unknown", is a related form of fallacy in which one attempts to prove something unknown by deducing it from something else which is also not known to be true.