 The knowledge of universals is reached through induction from the knowledge of singulars received through the senses (NLPA 171; DOS 196). Kilwardby describes the process in the following way: sensible species are retained in the absence of a sensible thing by memory, and from a multitude of memories arises experience, that is, a first comparison of what is common to the species, not yet a universal. The intellect is then able to discover the essential likeness (essentialis similitudo) or common nature (ratio uniuersalis) in which the sense data agree (NLP II.33, 503–504; DOS 7–8; NLPA 171–2). The universal is, then, the essential reason for agreement of many images of the same nature (QLIIS 78, 222.236–8; QLIIS 17, 71; Lewry 1978, 244).