  Grosseteste suggests that if the mind were healthy, and unaffected by the Fall, it would be able to see in God the exemplary forms of all the things he had created. But as it is, such knowledge of exemplary forms is impossible, though the light of God illumines the forms of particular things that we encounter in the world so that we can come to know them. Such forms are in themselves universal and unchanging (indeed, in themselves they are the same as, though not numerically identical with, exemplary forms), and so they can ground necessary truths. But the knowledge of a real definition of a substance, of a simple form, does not impart knowledge of its causal powers. (Ockham, it will be noted, shares this view.) For instance, the knowledge of the causal power of scammony to purge red bile arises only after we observe a number of cases where it does this, and so come to form an aestimatio that it does in this or that particular case. (An aestimatio is produced in the senses, and can be formed by irrational animals. It is a kind of perception of a particular causal conneciton, and is not necessarily correct. The idea seems to have come from Augustine, De Libero Arbitrio II.) Then, spurred on by this aestimatio, reason proposes an experiment, and introduces scammony when every other cause for the purging of red bile is absent, and if it often draws out red bile under these conditions, reason concludes that it is a causal power of scammony to do this. The intellect's ability to frame a universal concept after it becomes familiar with particular individuals through the senses is paralleled by its ability to form universal causal judgments after sensory aestimatio informs it of particular causal events. (Grosseteste (1981) I 14, lines 252-271.)