The primary matter is the indeterminate common nature, which needs a specific principle or form determining the substance that actually exists at any time. Prime matter is related to specific forms as potential is to actual. Matter without form is indescribable since only its form gives the specific differences whereby we can refer to any substance. The term is deployed in Aristotelian and scholastic thought in order to describe change in the physical world. Consider the way one substance (an acorn, a living body), may change into another (an oak tree or earth). There must be something common to the original and the later state, for otherwise the one would not change into the other, but would cease to exist and be replaced by something else entirely. The concept formed a major target for 17th-century proponents of the new scientific or corpuscularian view, such as Boyle and Locke, although perhaps ironically Locke is attacked by Berkeley for his adherence to a parallel notion of substance. See also hylomorphism, matter.