As was indicated, philosophers of the past, including Aristotelians and Illuminationists, considered motion to be specific to accidents. Not only did they fail to establish substantial motion, but they imagined it to be impossible. Also, among the ancient Greek philosophers none are to be found who explicitly discuss substantial motion or establish it. The only position which is comparable to substantial motion is that reported to have been held by Heraclitus (540-470 B.C.).
Other than those Islamic and non-Islamic philosophers and theologians who believed in constant renewing creation, none are found to whom a tendency toward substantial motion can be ascribed. However, contrary to the famous philosophers of the world, the one who explicitly established substantial motion and boldly insisted on it was the great Islamic philosopher, Sadr al-Muta’allihin Shirazi.
Here, we shall first present the objections raised by those who deny substantial motion and answer them, then we shall explain the theory of Sadr al- Muta’allihin and the arguments he has put forth to prove it.
The discussions of those who imagine substantial motion to be impossible turn on the notion that one of the prerequisites or rather one of the constituents, of every motion, is the existence of the moved, or in technical terms, the subject of motion.
When we say that the earth rotates on its axis and revolves around the sun, or that an apple turns from green to yellow and then to red, or that a sapling or a baby animal or human grows and develops, in each of these cases we have a fixed essence whose attributes and states gradually change.
However, if it is said that the essence itself is not fixed, and just as its attributes and accidents change, its substance also is transformed, then to what are we to relate this change? In other words, substantial motion will be a motion without a thing moved and an attribute without a thing to which attribution is made. This is not rational.
The origin of this objection is a defect in the analysis of motion. As a result, some philosophers, such as al-Shaykh al-Ishraq, have consciously considered motion to belong to the category of extraneous accidents, while others have unconsciously considered it so. Hence, they considered it necessary for there to be a entified independent subject of motion and attribution which remains fixed through the process of motion, and to which motion and change are related as accidents and attributes.
However, as was previously made clear, motion is that very flowing of the existence of substances and accidents, not an accident alongside other accidents. In other words, the concept of motion is not a whatish concept, rather it is a secondary philosophical intelligible. To put it still differently, motion is an analytic accident of existence, not an extraneous accident of existents.
These sorts of concepts do not need a subject in the sense which has been established for accidents. The only thing that can be considered as the source of abstraction of motion is the flowing substantial or accidental existence itself, in the sense of a subject related to analytic accidents, that is, a subject whose objective existence is identical with an accident, and any distinction between them is impossible except in the realm of mental analysis.
Therefore, when we say, ‘A substance has changed,’ it is as if we were to say, ‘the color of the apple (and not the apple itself) has changed.’ It is clear that in the process of a transformation in color, there is no fixed color to which the transformation is attributed. Even an independent subject is related to accidental motions only because of its being an accident, not because it is motion.
Therefore, even if the accident pertaining to the motion were to remain unchanged, it would still need a subject, as the apple itself is needed whether its color is fixed or changing.
It is to be concluded that motion and immutability are two analytic attributions for flowing and immutable existence, and such attributions do not require entified subjects of attribution independent of the attribution itself.
In the same way as immutability is not an accident of an existent in external reality in such a way that it would lack immutability without that accident, likewise, the attribute of motion is not is not an extraneous accident of a particular existent so that without it, it should be characterized with immutability and lack of motion. In technical terms, analytic accidents do not require independent subjects; rather their existence is identical with the existence of their subjects.
It is worth noting the subtle point that according to the fundamentality of existence, motion must be related to existence as an analytic accident, and the relating of it to the whatness of a substance or accident is an accidental relation.
Sadr al-Muta’allihin offered three lines of argument to establish substantial motion.
1. The first argument for substantial motion has two premises. One is that accidental changes in a thing are the effects of the substantial nature of that thing. The second premise is that the natural cause of motion must be a moving thing. From this it is concluded that a substance which is the cause of motion in accidents must be a moving thing.
As for the first premise, this is the famous principle indicated in the previous lesson, that is, the proximate and immediate agent of all motions is nature, and no motion can be directly related to an immaterial agent.
As for the second premise, it may be further explained that if the proximate and immediate cause of an effect were a stationary object, its result would also be a stationary.
In order to make this easier to understand, the following example may be used: if a lamp were in a fixed place the light which radiates from it would illuminate all within a specific radius, but if the lamp were in motion, the extent of its illumination would gradually advance. Hence, the process of moving accidents which advance in the realm of time shows that their cause also is in process along with them.
Perhaps it will be asked, if the nature of a substance is essentially in motion, then why are its effects, which are accidents, sometimes without motion? And why cannot the immobility of accidents be reason for the immobility of the nature of a substance?
These question can be answered as follows. The nature of a substance is not a complete cause of motion, rather, its effectiveness depends on specific conditions whose satisfaction brings about motions in accidents, and motion is an action which requires a natural agent, even if the agent is not the complete cause of its occurrence. Immobility, to the contrary, is a negative thing (the absence of motion), and cannot be considered to be an action in need of an agent.
On the other hand, it may be asked whether the proponents of substantial motion are not forced to relate substantial motion to immaterial agents, which are fixed, unchangeable and devoid of motion. Why do they not accept accidental motion for fixed substances as valid?
The answer is that substantial motion is the very existence of the substance, and is merely in need of a divine generative agent, and the granting of existence to the substance is the same as the granting of existence to the substantial motion. However, the granting of existence to the substance is not the same as the granting of existence to accidents and to motion in accidents.
For this reason, the motion in accidents is related to substantial nature, and is considered an action for it. Such an action is in need of a natural agent whose transformation shows a transformation in its agent.
Another very precise objection can also be raised against this argument, the answer to which is not as easy as the answer to the previous two objections. According to Sadr al-Muta’allihin’s own explanation, motion is not a entified object independent of its source of abstraction, the flowing existence of a substance or accident. Hence, whether it is assumed to be in a substance or in an accident, motion will be the same as the existence of that substance or accident, and its cause will be the cause of the existence of that substance or accident.
Therefore, what prevents us from relating the flowing existence of an accident directly to a divine or metaphysical agent and to consider the role of substance in its occurrence as the role of matter for the occurrence of form rather than as the efficient cause (‘illat fa‘ili)? If this assumption is correct, there will be no way to infer substantial motion from the agency of substance for its accidents and their motions. In fact, this objection arises from doubts about the first premise.
But, in any case, this argument at most will be of benefit to those who consider the agency of substantial nature for their accidents and motions to be debatable.
2. The second argument also has two premises. One is that accidents do not have existence independent of their subjects, but rather they are really aspects of the existence of substance. The second premise is that every kind of change that occurs in an aspect of an existent, is a change in the existent itself, and indicates its own internal and essential change. It is concluded that motions in accidents indicate changes in the existence of a substance.
In explaining this argument, Sadr al-Muta’allihin says that every corporeal existent has a single existence which is in itself determinate and individual (as was explained in Lesson Twenty-Five). The accidents of every substance are appearances or rays of its existence, which may be considered signs of individuation (‘alamat tashakhkhus) for it and not as causes of its individuation. Therefore, a change in these signs indicates a change in that which bears the sign; hence, motion in accidents indicates motion in the existence of a substance.
This argument does not depend on the assumption that motion in accidents is an effect of substantial nature, but rather accidents are introduced as appearances and aspects of the existence of a substance. This position is acceptable in the case of continuous quantities because the dimensions and extensions of corporeal existents are nothing but their visages, as was explained in Lesson Forty-Seven.
It can also be applied in the case of qualities specific to quantity, such as geometrical shapes. However, relative categories, as was mentioned repeatedly, are abstract concepts and only the source of abstraction of some of them, such as time and space, can be considered to be aspects of the existence of substance, which reduce to continuous quantities.
The existence of psychic (nafsani) qualities (which in a precise sense are objective accidents, although in a sense they may be considered to be appearances and aspects of the psyche) is not the same as the existence of the psyche. Rather, there is a sort of union (not unity) between these qualities and the psyche, and for this reason, the application of this argument for such accidents is difficult.
3. The third argument given by Sadr al-Muta’allihin for substantial motion is obtained from knowledge of the reality of time as a flowing and passing dimension of material existents, and the logical form of this argument is as follows.
All material existents are in time and have a temporal dimension. Every existent which has a temporal dimension has gradual existence. In conclusion, the existence of a material substance will be gradual, that is, possessing motion.
The first premise was made clear in Forty-Three, from which it may be concluded that time is the passing extension of corporeal existence, not an independent vessel in which they are contained. If material phenomena did not have such a passing extension, they could not be measured with temporal scales, such as clocks, days, months and years.
Likewise, if they did not have spatial extensions and geometrical dimensions, they could not be measured by length, area and volume. Basically, the measurement of everything by a specific scale shows the homogeneity between them. Therefore, the weight of something can never be measured by the scale of length or vice versa.
It is for this reason that completely immaterial things do not have a temporal duration, and they cannot be considered temporally prior to or posterior to an event, for their immutable existences are not homogeneous with the passing and renewing extension of time.
The second premise can be explained as follows. Time is passing so that its potential parts are brought about successively. One part of it does not occur until another part passes, while the entirety of its supposed parts has a single existence.
It we understand the nature (haqiqat) of time; we will readily discover that every existent which possesses this sort of extension in its essence will have a gradual existence and will have parts spread out in the channel of time. Its temporal extension is divisible into successive potential parts no two of which can be brought together. Until one of them passes and is annihilated another part will not be brought into existence.
Given these two premises, it can be concluded that the existence of a corporeal substance is gradual, passing, and constantly renewed, and this is the meaning of substantial motion.
In explaining this argument, Sadr al-Muta’allihin says that just as a material substance has geometrical and spatial dimensions, it also has another continuous quantity called time (which constitutes its fourth dimension), and just as its instantaneous extension is an essential attribute of its existence, and has no existence separate from that of the material substance, likewise its gradual extension is an inseparable and essential attribute for it.
And just as the individual ipseity of a corporeal substance is never brought about without geometrical dimensions, likewise it cannot occur without the temporal dimension. No corporeal substance can be imagined to be fixed and detached from time, and therefore as related equally to all times. So, time is a constituent of the existence of every corporeal substance. This implies that the existence of every corporeal substance is gradual and that its supposed parts are brought into existence successively and by constant renewal.
This argument is the firmest of the arguments for substantial motion, and there appear to be no problems with it.