Part 7Chapter Summaries & Analyses
Part 7: “Book 7—Various Points About Change”
Part 7, Chapter 1 Summary: “Everything That Changes Is Changed by Something”
Aristotle argues that “everything that changes must be changed by something” (167). If the source of change is not within the object itself, then the cause is something external. Even if the source appears to be within the object, the claim that a thing changes entirely by itself is problematic. A changing object is divisible into parts. If one part of it remains unchanged while another part changes, the whole object cannot be said to change in its own right. Therefore, the change must depend on something else that causes or sustains the process. From this reasoning, Aristotle concludes that every change requires a “mover” (168).
Aristotle then considers whether the chain of movers could extend infinitely. Suppose one object is moved by another, which is moved by another and so on without limit. In that case, all the movements in the series would occur simultaneously, because each mover moves while being moved by another. If the chain were infinite, the total movement would also be infinite. However, the movement of the first object occurs within a finite time. This would imply that an infinite movement takes place in a finite time, which Aristotle regards as impossible. He also notes that—in cases of physical movement—the mover and the moved object must be in contact or continuous with one another.
Therefore, the entire sequence of movers and moved objects forms a single connected magnitude. If the chain were infinite, that magnitude would also be infinite and it would be traversed in a finite time, which is impossible. Aristotle therefore concludes that the sequence of movers cannot regress infinitely and “there must be a first thing which moves others by being moved itself” (170).
Part 7, Chapter 2 Summary: “The Agent of Change and the Object Changed Must Be in Contact”
Aristotle argues that the immediate agent of change must be in contact with the object that is changed. By “immediate agent” (170), he means the direct source of the change rather than the purpose or final cause. Between the agent and the changed object, there can be nothing intermediate. This principle applies to all types of change. He identifies three principal kinds of change: Change of place, change of quality, and change of quantity. Correspondingly, there are agents that cause movement, alteration, and increase or decrease.
Aristotle begins with movement, which he treats as the most basic type. When something moves, it is either self-moved or moved by something else. In the case of self-movement, the mover is within the object itself, so the mover and the moved part are already contiguous. When motion is caused externally, it occurs through four basic modes: Pulling, pushing, carrying, and rotating. Aristotle argues that all locomotion can ultimately be reduced to these four forms and that pushing and pulling are fundamental among them.
In each case, the mover must be contiguous with the object moved. The definitions of pushing and pulling imply physical contact, since they involve moving something away from or toward a source. Therefore, no gap can exist between the mover and the object moved. Aristotle extends the same reasoning to other kinds of change. In alteration, the agent and the affected object are contiguous because change occurs through perceptible qualities such as heat, sweetness, dryness, or color. Sensory processes illustrate this: Light connects color with the organ of sight, air connects sound with hearing, and flavor is contiguous with the organ of taste. Similarly, increase and decrease occur through addition or subtraction of parts, which also requires continuity between agent and object. From these examples, Aristotle concludes that in every type of change, the immediate agent and the object changed must be contiguous, with “nothing between them” (173).
Part 7, Chapter 3 Summary: “Only Perceptible Qualities Can Be Altered or Can Alter Other Things”
Aristotle argues that only perceptible qualities can properly undergo alteration or cause alteration. He examines other possible candidates—such as shapes, structures, and states—and concludes that these are not alterations. When something acquires a form, such as a statue or a house, people describe the object by reference to its material in a modified way, which shows that generation of form differs from alteration. The coming into being of shapes therefore is not alteration, even if alterations of matter precede it.
Aristotle also argues that bodily and mental states are not alterations. Good states represent completion, while bad states represent a departure from completion. These states arise through relations among bodily elements and their interactions with perceptible things. Although alterations of bodily elements may lead to the acquisition or loss of such states, the states themselves are not alterations. Similarly, intellectual states are not alterations. Knowledge arises when the mind reaches a state of rest rather than through a process of alteration. Aristotle concludes that true alteration occurs only in perceptible qualities and in the perceptive part of the mind.
Part 7, Chapter 4 Summary: “When Is One Change Faster Than Another?”
Aristotle examines whether different kinds of change can be compared in terms of speed. He notes that if two changes were said to have the same speed whenever they complete equal amounts of change in equal time, this would imply that different kinds of changes, such as alteration and movement, could be compared directly. That would lead to the “absurd” (178) conclusion that an affection could be equal to a distance. He therefore argues that not all changes are comparable. Comparison is possible only when the changes belong to the same species and involve the same kind of attribute. Movements along different kinds of paths—such as circular and straight lines—cannot be compared if the paths themselves are specifically different. Likewise, alterations involving different qualities cannot be directly compared.
Within a single species of change, however, comparisons are possible. For example, two processes of recovery may be said to occur at the same speed if they reach the same state in the same time. Aristotle believes that comparisons of speed apply only within the same species of change and when the relevant attributes and subjects are the same.
Part 7, Chapter 5 Summary: “Concerning the Proportion: Power Acting Is to Weight Moved as Distance Moved Is to Time Taken”
Aristotle analyzes the proportional relations involved in motion. Any agent that moves something does so over a certain distance and within a certain time. The same power moving half the weight can move it a greater distance in the same time, or the same distance in less time. Similarly, a power half as strong can move half the weight the same distance in the same time. The ratios between power, weight, distance, and time therefore remain consistent.
However, a weaker power does not necessarily move the same weight proportionally. Half the power might fail to move the object at all. Aristotle illustrates this with the example that one person alone cannot move a ship that many people together can move. He also rejects Zeno’s claim that a single grain of millet must produce sound like a falling bushel. He concludes that similar proportional relations apply to alteration and increase, where agents act on subjects in measurable degrees over time.
Part 7 Analysis
In Book 7, Aristotle invokes the image of a chain of movers, which introduces his interest in The Unmoved Mover and Eternal Motion. This imagery illustrates his point about the nature of the infinite. While his earlier use of imagery and metaphor were meant to prove a positive point about his ideas, this particular image is presented with the intent of proving a negative. The image of the chain of movers, Aristotle suggests, is inherently absurd and unworkable. He is deliberately invoking the idea of the impossible in his attempt to assert a logical position. This rhetorical method suggests that Aristotle is moving away from the fixed positions of his earlier chapters and toward something more abstract as his ideas become increasingly complex.
At the same time, Aristotle’s writing has begun to incorporate more formulae. Though he does not stray into outright mathematics or calculation, Aristotle relies on compositions like formulae to prove his logical points. When describing the relationship between three separate entities or ideas, for example, he chooses to label them as A, B, and C. Thus, this academic shorthand for his ideas comes to resemble a mathematical formula even though Aristotle himself has attempted to distance natural science from mathematics. This incorporation of formulae shows how Aristotle’s complex ideas are contained within a broader philosophical framework, however.
Book 7 also contains another reference to the unworkable nature of one of Zeno’s ideas. Though this only comes in the closing chapter, Aristotle’s rebuke of Zeno’s claim that a single grain of millet must produce sound like a falling bushel is treated with contempt. Again, Zeno emerges as something of an antagonistic figure in Aristotle’s discussion. Aristotle cannot help but throw a sideways criticism at Zeno once again, even after thoroughly debunking the so-called paradoxes in earlier chapters. Zeno alone receives this treatment from Aristotle, which is suggestive of Zeno’s incompatibility with Aristotle’s approach.
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