  In the third section, al-Kindi first proves that nothing can be its own cause, a point that is not used explicitly in what follows, but may be intended to show that nothing can be the cause of its own unity. He then undertakes an exhaustive survey of the various types of “utterance (lafz).” Following Porphyry’s Isagoge, he classifies all predicates or terms (maqulat) into genus, species, difference, individual, proper accident, and common accident. Taking them in turn, al-Kindi argues that each type of predicate implies both unity and multiplicity. For example, animal is one genus, but it is made up of a multiplicity of species; human is one species but is made up of many individuals; and a single human is one individual but made up of many bodily parts. Finally, al-Kindi seeks an explanation for the association of unity and multiplicity in all these things. He argues that the association cannot be merely the product of chance; nor can it be caused by any part of the set of things that are both one and many.  So there must be some external cause for the association of unity and multiplicity. This cause will be exclusively one, entirely free of multiplicity: al-Kindi expresses this by saying that it is “essentially” one, whereas the other things are “accidentally” one. He also speaks of it as “one in truth,” whereas other things are one “metaphorically.” In short, the cause in question is the “true One,” or God.