  Duns Scotus seems to have retained Grosseteste's empiricist bent. Some causal principles are known per se, for instance, that an opaque thing placed between something illuminated and its light source will block the light and leave that thing in the dark. Here, anyone who knows the definitions of the terms (in the example, of ‘opaque’) can work out the principle from there. But, like Grosseteste, he also thought some principles can only be discovered through experience. So he advances the notion that “Whatever occurs in many instances by a cause that is not free is the natural effect of that cause.” He seems to assume that a sufficient number of observations will lead to cases in which the cause fails, if it ever does. In any case, this seems to continue Grosseteste's empiricist tendencies, for he apparently assumes that a simple substance must be observed to function before one can conclude through reason that it functions as it does. Aquinas would no doubt say that such observation of the immediate functioning of a simple substance is necessary in order to acquire a concept of its substantial nature, and so its real definition. A real definition of a substance will specify its natural effect, and we do not infer its functioning from experience, but rather use experience to abstract its real definition.