To the modulus. In mathematics, two numbers are said to be congruent modulo n when they differ by some multiple of n. For instance, 40 is congruent to each of 24 and 32 modulo 8. In Quine’s Word and Object the modulus of a stimulus is its duration, and two stimuli may be equivalent modulo one duration, but not modulo another. Other uses of the term have been temporarily fashionable in philosophy, and have to be picked up, if possible, from the context.