Partial structures and Jeffrey-Keynes algebras

In Tsuji 1997 the concept of Jeffrey-Keynes algebras was introduced in orde r to construct a paraconsistent theory of decision under uncertainty. In th e present paper we show that these algebras can be used to develop a theory of decision under uncertainty that measures the degree of belief on the qu asi (or partial) truth of the propositions. As applications of this new the ory of decision, we use it to analyze Popper's paradox of ideal evidence an d to indicate a possible way of formalizing Keynes' theory of economic acti on.