  How it executes those functions is expressed in principles per se in the second way, so that the subject is somehow implicated in the predicate. It is in these first principles that natural causes are expressed. Grosseteste supposes that we have a faculty, aestimatio, parallel to the senses, which enables us to simply see a particular causal connection. This faculty is no more infallible than are the senses, but after a number of such experiences of a causal relation the intellect will be aroused, and will begin to seek actively whether the apparent causal connection is real or not. To do this, it will attempt to produce experiences in which the apparent cause is present, but nothing else that might be a cause is. If the effect is produced in such situations, it will then conclude the first principle, which will assert the material definition of the attribute to its formal definition. For instance, through experience we might note that thunder is caused by the extinction of fire, and express this in the principle that thunder, considered formally (as a noise in a cloud, perhaps with a certain function of frightening those in Hades), is in fact the same as noise in a cloud produced by the extinction of fire (the material realization of this function of frightening by a loud noise). Or we might note that anger (as the desire to harm someone) is in fact, in this world, the same thing as the boiling of blood around the heart (the material conditions for its realization). Thus he takes causal principles to describe how a form is realized (made actual) given certain material resources. To see what material resources in fact realize the form, sensory experience, aided by reason, is needed.