Out of Context: On Logic (Definitions)

"Logic is the procession or proportionate unfolding of the intuition; but its virtue is as silent method; the moment it would appear as propositions, and have a separate value, it is worthless." (Ralph W Emerson, "Essays", 1841)

"The actual science of logic is conversant at present only with things either certain, impossible, or entirely doubtful, none of which (fortunately) we have to reason on." (James C Maxwell, 1850)

"Logic, then, is not necessarily an instrument for finding truth; on the contrary, truth is necessarily an instrument for using logic - for using it, that is, for the discovery of further truth and for the profit of humanity. Briefly, you can only find truth with logic if you have already found truth without it." (Gilbert K Chesterton, Daily News, 1905)

"Symbolic Logic is Mathematics, Mathematics is Symbolic Logic, the twain are one." (Cassius J Keyser, "Lectures on Science, Philosophy and Art", 1908)

"[...] logic, or the science of concepts, is that system which studies the qualitative (categorical) relations between things." (Peter D Ouspensky, "Tertium Organum: The Third Canon of Thought; a Key to the Enigmas of the World", 1922)

"In other words, logic is concerned with the context of justification." (Hans Reichenbach, "The Rise of Scientific Philosophy", 1951)

"Logic and truth are two very different things, but they often look the same to the mind that’s performing the logic." (Theodore Sturgeon, "More Than Human", 1953)

"[Fuzzy logic is] a logic whose distinguishing features are (1) fuzzy truth-values expressed in linguistic terms, e. g., true, very true, more or less true, or somewhat true, false, nor very true and not very false, etc.; (2) imprecise truth tables; and (3) rules of inference whose validity is relative to a context rather than exact." (Lotfi A Zadeh, "Fuzzy logic and approximate reasoning", 1975)

"Logic is the theory of inference and argument." (Ian Hacking, "The Taming of Chance", 1990)

"Logic is the study of methods and principles of reasoning, where reasoning means obtaining new propositions from existing propositions." (Huaguang Zhang & Derong Liu, "Fuzzy Modeling and Fuzzy Control", 2006)

"Fuzzy logic is an application area of fuzzy set theory dealing with uncertainty in reasoning." (Larbi Esmahi et al,  Adaptive Neuro-Fuzzy Systems, 2009)