 To the best of our knowledge, the doctrine of qualities is first stated by Galileo Galilei. A paradigm-destroying natural philosopher for whom “the book of nature is written in the language of mathematics” (Galileo 1623 [2008: 179–83]; Crombie 1972). Galileo argues for the distinction in a section of The Assayer (1623). Having been asked to explain why he thinks it may be possible that motion is the cause of heat, he produces a non-technical sample of his distinctive method of answering questions that arise in natural philosophy. The general method relies on intellect, thought experiments, hypotheses about things that are quantifiable, and sense perception of measurements that may testify to their reality (Crombie 1972: 72–4, 81–7; Piccolino and Wade 2008, passim)). The argument goes as follows. We cannot conceive a corporeal substance without a determinate figure, size, position, motion/rest, and number; nor can we imagine bodies separated from any of these attributes. Galileo calls them “primary affections” of matter. By contrast, it is not necessary to conceive that a body have a color, taste, aroma, or make a sound; if we lacked senses, intellect and imagination might never think of them.