(3) A sensation is that which comes to the mind through the senses.
FOURTH RULE.
A definition must not be expressed in obscure, figurative or ambiguous language.
A violation of this rule is referred to in logic as “defining the unknown by the still more unknown” (ignotum per ignotius).
It is known that the purpose of definition is to make clear some obscure term, consequently unless every word used is understood the chief aim of the definition has been defeated.
From this it must not be inferred that all definitions should be free from technical terms. Such a restriction would make the defining of many terms unsatisfactory and in a few cases practically impossible. To the student of evolution the following definition by Spencer is intelligible while to the uninitiated it would appear obscure: “Evolution is a continuous change from an indefinite, incoherent homogeneity to a definite coherent heterogeneity through successive differentiations and integrations.”
This rule insists upon simple language when it is possible to use such in giving an accurate and comprehensive meaning to the term defined.
Illogical Definitions According to the Fourth Rule.
(1) “A net is something which is reticulated and decussated, with interstices between the intersections.” Dr. Johnson.
(2) “Thought is only a cognition of the necessary relations of our concepts.”