 In two remarkable papers, the short note 1883 and the longer “On the Algebra of Logic” of 1885, he introduced a modern notation for what he was the first to call the “quantifier”. He viewed his quantifiers (for which he used the symbols \(\Pi\) and \(\Sigma)\) as a generalization of the Boolean connectives, with the universal quantifier \(\Pi\) being interpreted as a (possibly infinite) conjunction, so that \(\Pi_x P(x)\) is understood as “a is P and b is P and c is P and …”. Similarly the existential quantifier \(\Sigma\) is understood as a (possibly infinite) sum: “a is P or b is P or c is P or …”. This flexible \(\Pi\) and \(\Sigma\) notation allowed him easily to express nested quantifications to any desired depth. Thus, in his notation, if \(l_{ij}\) represents “i is a lover of j”, \(\Sigma_i \Sigma_j\) \(l_{ij}\) tells us that somebody loves somebody, whereas \(\Pi_i \Sigma_j\) \(l_{ij}\) tells us that everybody loves somebody. (The \(\Sigma\) and \(\Pi\) notation is of course intended, in a Boolean spirit, to emphasize the analogy to arithmetical sums and products.)