Abstract: To the predicate calculus on Intuitionistic Fuzzy Logic (IFL), a symmetric synthetic method for finding the truth of IFL propositions using membership and hesitancy degree is proposed on the basis of the hypothesis of an equilibrium state of supportability and opposability of neutral evidences indicated in the intuitionistic index. The fundamental operation rules on IFL propositions are presented. The investigation is with an emphasis on the techniques for conditional reasoning on IFL, including the implications, the conditions, the multiplications, and the multi-dimensions on IFL, etc. The related sets of mathematical formulas of inference compositional operations are derived. To the IFL reasoning with confidence factors, including those of the typical, the weighted, and the narrow senses, the effects of confidence factors spreading abroad in rules on those of conclusions are analyzed. The related formulas for finding the true conclusions are exposed.