Fuzzy set theory and fuzzy logic has been initiated by Zadeh back in 1965 to pennit the treatment of vague, imprecise, and ill-defined knowledge in an concise manner. One of the unique advantages of fuzzy logic is that it is capable of directly incorporating and utilizing qualitative and heuristic knowledge in the form of causal if then production rules for reasoning and inference. On the other hand, rule-based speech synthesis based on formants makes considerable use of rules for numerous of the tasks it involves, e.g. graphemic to phonemic transcription, coarticulation, concatenation, and duration rules etc. These rules also take the if then form with their antecedent (condition) part describing the context of the rule and their decedent an appropriate action to be taken. The main motivation for introducing fuzzy logic in the synthesis-by-rule paradigm, is its ability to host and treat uncertainty and imprecision both in the condition part of the rule as well as its decedent part. This may be argued to significantly reduce the number of required rules while rendering them more meaningful and human-like.