 It is an important property of Łukasiewicz’s three-valued logic that the truth-value of the disjunction of two undetermined propositions is undetermined, i.e., \((p \vee q)\) is undetermined for \(p\) undetermined and \(q\) undetermined. This may be based on the observation that since \(p \equiv(p \vee p)\), a disjunction of two undetermined propositions has to be undetermined. If \(p\) is undetermined, \({\sim}p\) is also undetermined. It follows that \((p \vee{\sim}p)\) is undetermined for \(p\) undetermined. This problem also occurs for future contingents such as \(F(x)q\) and \(F(x){\sim}q\). According to Łukasiewicz’s trivalent logic: if \(F(x)q\) and \(F(x){\sim}q\) are two future contingents, i.e., if they are both undetermined, then the same will be the case for the disjunction of the two statements, \(F(x)q \vee F(x){\sim}q\). This means that the theory leads to the rejection of the principle of (P5).