• Essay Concerning
    Human Understanding
    (1690, 4th ed. 1700)

While some ideas have a natural corrispondence and connexion with each other "there is another Connexion of Ideas wholly owing to Chance or Custom; Ideas that in themselves are not all of kin, come to be so united in some Men's Mind, that 'tis very hard to separate them, they always keep in company, and the one no sooner at any time comes into Understanding but his Associate appears with it; and if they are more than two thus united, the whole gang always inseparable shew themselves together" (II, xxxiii).