 On this basis Łukasiewicz develops a calculus of truth-values in which he can deal with logically complex propositions, conditional probability, probabilistic independence, and derive Bayes’ Theorem. The calculus of truth-values is used as a logical theory of probability, assisting us in our dealings with definite reality: Łukasiewicz denies that there can be a theory either of objective or of subjective probability as such. Two ideas from this short but remarkable work are worth emphasizing because they resonate with later ones of Łukasiewicz. Firstly, there is the idea of a proposition (in this case an indefinite proposition) being neither true nor false; secondly, and connected with this, of such a proposition having a numerical truth-value properly between 0 (false) and 1 (true). Łukasiewicz’s theory deserves to be better known: it continues and extends earlier ideas of Bolzano, his probability corresponding to the latter’s degree of validity of a proposition (with respect to variable components). Its chief drawback is that it is formulated for finite domains only.