a composite definition, even though it mentions both the accident and the substance’s receptivity to it; for the sole aim of the definition is to highlight receptivity.
Composition itself is of two kinds: one that is invalid by consensus and another that is disputed. What is unanimously rejected is when the definer cites two notions, either of which would suffice on its own, so that mentioning the second is mere redundancy with respect to the goal and criteria of a definition. The disputed type is exemplified by the Muʿtazilites when they define the visible as “that which is a colour or is coloured.” They regard this as a sound definition and see no flaw in the composition. Their argument is that the purpose of a definition is to circumscribe the definiendum while engaging its reality. Proof has established that what occupies space is seen and that colours are visible, yet colours and substances do not share a single reality, for the attributes common to them—such as existence or origination—are too general. Defining the visible as “existent” or “originated” would entail that tastes, smells, items of knowledge, and the like are visible as well. Since it is impossible to gather substances and colours under one non-vitiating attribute that bears on visibility, nothing remains but to mention substances by their own distinctive character and colours by their own essential reality.
Most theologians, however, refuse to allow such composition in definitions. They contend that “occupying space” and “being a chromatic quality” are two mutually exclusive rulings; therefore, given their divergence, it is improper to assign them a judgment that admits no divergence—namely, being visible.
Al-Ustadh Abū al-Maʿālī said:
“The best manner of handling this issue is what the Qadi has stated, for he says:
‘The material dealing with the knowledge of definitions is of two kinds. Sometimes it is possible to encompass every individual instance of the definiendum by means of a single attribute shared by them all—such as our defining knowledge by “cognition” or thingness by “existence.” At other times it is impossible to encompass all instances under one common attribute; if one were to cite such an all-inclusive attribute, the definition would be invalid. In that case, if what is being inquired about can be delimited by mentioning two attributes—one of which covers one group of instances and the other covers the rest—the definition is sound.’”
The Qadi continued: “If this point were thoroughly examined, the dispute would disappear, for the person who defines by two attributes—were he asked, ‘Do you claim