  In both On the Soul and On the Universe William attacks at length theories of cognition that posit an agent intellect or agent intelligence. He incorrectly ascribes the latter theory to Aristotle, although in fact it is Avicenna's teaching; he ascribes the former theory to certain unnamed contemporaries. These theories view cognition as involving the active impression of intelligible signs or forms—what we might call concepts—on a receptive or passive recipient. The agent intellect or agent intelligence is taken to perform this function of impressing intelligible forms on our material intellect, which is so-called because like matter it is receptive of forms, albeit intelligible forms. The chief difference between the agent intellect and agent intelligence, as far as the theory of cognition is concerned, is that the former is treated as a part of the human soul, while the latter is taken to be a spiritual substance apart from the human soul, identified with Avicenna's tenth intelligence. William notes how the agent intellect or agent intelligence is viewed by analogy with light or the sun; as light or the sun through its light serves to render actual merely potentially existing colors, so the agent intellect or intelligence serves to render actual intelligible forms existing potentially in the material intellect.