Nihil est in intellectu quod non prius fuerit in sensu (Latin, ‘Nothing is in the understanding that had not previously been in the senses’), a principal tenet of empiricism. A weak interpretation of the principle maintains that all concepts are acquired from sensory experience; no concepts are innate or a priori. A stronger interpretation adds that all propositional knowledge is derived from sense experience. The weak interpretation was held by Aquinas and Locke, who thought nevertheless that we can know some propositions to be true in virtue of the relations between the concepts involved. The stronger interpretation was endorsed by J. S. Mill, who argued that even the truths of mathematics are inductively based on experience. See also EMPIRICIS. W.E.M.