The ancient philosophers did not hold that light and heat...

The ancient philosophers did not hold that light and heat had any reality apart from the states and accidents which are perceived by the sensory organs, and in this respect they considered them to be essentially simple and unanalyzable.

However, on the basis of some views in modern physics, they must be considered to be material substances, and however much they are called energy as opposed to matter in the terminology of physics, since it is believed that matter comes into existence through the concentration of energy and turns into energy through decomposition and radiation, from a philosophical perspective, energy must be considered a kind of body.

It is impossible for a body to be composed of something other than bodies or to change through decomposition into something other than extended substance (i. e., body). The issue is not settled with this, and with further attention it becomes clear that what is perceived directly is not the substance of light and heat, but an attribute of luminosity and heat.

Here the previous question may be repeated as to whether the sensible qualities exist in the external world in the same way that they are reflected in the realm of perception. Qualities Specific to Quantities Philosophers have also named another group of qualities as qualities specific to quantities. One group of them, such as oddness and evenness, are attributes of number. Another group, such as straightness and curvature, are attributes of geometrical subjects.

Apparently, the reason these qualities are considered to be an independent group and not sensible qualities is that they are not perceived directly by the senses. The attributes of numbers cannot be considered to be real things and objective accidents, given that number itself is respectival ( i‘tibārī ) and lacks an object in the external world.

However, the attributes of geometrical subjects, such as the straightness and curvature of a line, or the flatness, concavity and convexity of a plane are abstracted concepts, abstracted from the mode of existence of bodies by several intermediaries. This is especially so, given that line and plane themselves are negative limits ( ḥudūd ‘adamī ) of bodies without any real existence of their own, which the human mind loosely considers to be whatnesses existing in the external world.

Therefore, it is difficult to consider this group of qualities as objective accidents possessing entified objects. At most they may be considered to be analytic accidents.