logical product a conjunction of propositions or predicates. The term ‘product’ derives from an analogy that conjunction bears to arithmetic multiplication, and that appears very explicitly in an algebraic logic such as a Boolean algebra. In the same way, ‘logical sum’ usually means the disjunction of propositions or predicates, and the term ‘sum’ derives from an analogy that disjunction bears with arithmetic addition. In the logical literature of the nineteenth century, e.g. in the works of Peirce, ‘logical product’ and ‘logical sum’ often refer to the relative product and relative sum, respectively. In the work of George Boole, ‘logical sum’ indicates an operation that corresponds not to disjunction but rather to the exclusive ‘or’. The use of ‘logical sum’ in its contemporary sense was introduced by John Venn and then adopted and promulgated by Peirce. ‘Relative product’ was introduced by Augustus De Morgan and also adopted and promulgated by Peirce. R.W.B.