From Fuzzy Thinking, by Bart Kosko (p. 19):
“Logicians in the 1920s and 1930s first worked out multivalued logic to deal with Heisenberg‘s uncertainty principle in quantum mechanics, … This math principle says that if you measure some things precisely, you cannot measure other things as precisely. This principle suggests that we really deal with three-valued logic: statements that are, true, false or indeterminate. In short order Polish logician Jan Lukasiewicz chopped the middle “indeterminate” ground into multiple pieces and came up with many-valued or multivalued logic. Lukasiewicz then made the next step and let indeterminacy define a continuum, a spectrum between falsehood and truth, between 0 and 1… The term “fuzzy” entered the scientific vocabulary about 30 years later. Until then logicians like Bertrand Russell used the term “vagueness” to describe multivalence.