Analyticity and circularity

"No bachelor is married" can be turned into "No unmarried man is married" because "bachelor" is defined as "unmarried man". But, Quine asks: how do we find out that "bachelor" is defined as "unmarried man"? Clearly, a dictionary would not solve the problem, as a dictionary is a report of already known synonyms, and thus is dependent on the notion of synonymy, which Quine holds as unexplained.

http://en.wikipedia.org/wiki/Two_Dogmas_of_Empiricism

• In Chapter 19, Definition 1, Leibniz writes: "Two terms are the same (eadem) if one can be substituted for the other without altering the truth of any statement (salva veritate)."
• In Chapter 20, Definition 1, Leibniz writes: "Terms which can be substituted for one another wherever we please without altering the truth of any statement (salva veritate), are the same (eadem) or coincident (coincidentia). For example, 'triangle' and 'trilateral', for in every proposition demonstrated by Euclid concerning 'triangle', 'trilateral' can be substitutedwithout loss of truth (salva veritate)."

The literal translation of the Latin "salva veritate" is "with unharmed truth", using ablative of manner.