Online research in philosophy

This article takes as its point of departure the conviction that late medieval science should be studied in its own right, and not merely to determine whether it presaged developments in early modern science. Case in point: Francis of Marchia's theory of virtus derelicta, the theory that the motion of a projectile through the air is due to a force left behind by the original motive force. Certainly, Marchia's view is not a forerunner of inertia. Nevertheless, it is argued that virtus derelicta breaks with two important Aristotelian principles of motion: "everything that has a beginning must necessarily also have an end" and "form is always indivisible." Thus, virtus derelicta is neither an Aristotelian solution to the problem of projectile motion nor a development on the road to early modern science; it belongs to a new (but subsequently undeveloped) understanding of motion.

Inertia is enshrined in Newton’s first law of motion, a body at rest or in uniform motion remains in that state unless a force is applied to it. Now, consider (1). (1) Pat stopped the car before it hit the tree. Can we conclude from (1) that the car struck the tree? Not without further information such as that supplied in (2). (2) But the bus behind kept going. A post-condition for Pat stopping the car is that the car be at rest. To satisfy a pre-condition for the car hitting the tree (namely, that the car not be at rest), inertia requires that some intervening force act on the car (as hinted, for example, by (2)). In the absence of such a force, (1) would appear to suggest that Pat prevented a collision between car and tree. Exactly what bit of physics are we importing into natural language interpretation here? Oversimplified, Newton’s first law of motion says: no change without force. Identifying force with cause, we come to the slogan no temporality without cause, capturing in a phrase the proposal from Steedman 2000 that..

A conservation principles tell us that some quantity, quality, or aspect remains constant through change. Such principles appear already in ancient and medieval natural philosophy. In one important strand of Greek cosmology, the rotatory motion of the celestial orbs is eternal and immutable. In optics, from at least the time of Euclid, the angle of reflection is equal to the angle of incidence when a ray of light is reflected. According to some versions of the medieval impetus theory of motion, impetus remains in a projected body (and the associated motion persists) permanently unless the body is subject to outside interference. These examples could be multiplied. But it was in the seventeenth century that conservation principles began to play an absolutely central role in scientific theories. Each of Galileo Galilei, René Descartes, Christiaan Huygens, Gottfried Leibniz, and Isaac Newton founded his approach to physics upon the principle of inertia—that unless interfered with a body will undergo uniform rectilinear motion. A multitude of other conservation principles gained currency during the seventeenth century—some still with us, some long ago left behind. Descartes provides an interesting example of an author who attempted to derive all of his physical principles from conservation laws (Principles of Philosophy, see especially articles 36 to 42 of Part II). Descartes believed that the principles of his physics could be derived from the immutability of God, supplemented only by very weak assumptions about the existence of change in the world. He claims, in fact, that we ought to postulate the strongest conservation laws consistent with such change. These include.

Here I reexamine Duhem's question of the continuity between medieval dynamics and early modern conservation theories. I concentrate on the heavens. For Aristotle, the motions of the heavens are eternally constant (and thus mathematizable) because an eternally constant divine Reason is their mover. Duhem thought that impetus and conservation theories, by extending sublunar mechanics to the heavens, made a divine renewer of motion redundant. By contrast, I show how Descartes derives his law of conservation by extending Aristotelian celestial dynamics to the earth. Descartes argues that motion is intrinsically linear, not circular. But he agrees that motion is mathematically intelligible only where divine Reason moves bodies in a constant and eternal motion. Descartes strips bodies of active powers, leaving God as the only natural mover; thus both celestial and sublunar motions are constant, and uniformly mathematizable. The law of conservation of the total quantity of motion is an attempt to harmonize the constancy derived a priori with the phenomenal inconstancy of sublunar motions.

There is considerable debate among scholars over whether Descartes allowed for genuine body-body interaction. I begin by considering Michael Della Rocca's recent claim that Descartes accepted such interaction, and that his doctrine of the creation of the eternal truths indicates how this interaction could be acceptable to him. Though I agree that Descartes was inclined to accept real bodily causes of motion, I differ from Della Rocca in emphasizing that his ontology ultimately does not allow for them. This is not the end of the story however, since two of Descartes's successors offered incompatible ways of developing his conflicted account of motion. I contrast the occasionalist view of Nicolas Malebranche that changes in motion derive directly from divine volitions with the non-occasionalist claim of Pierre-Sylvain Regis that such changes derive from a nature distinct from God. In light of Della Rocca's interpretation, it is noteworthy that the issue of eternal truths is relevant to both alternative accounts. Indeed, Regis took the doctrine that such truths are created to provide crucial support for his alternative to an occasionalist account of body-body interaction. What does not help Della Rocca, however, is that Regis's view of motion requires a fundamental revision of Descartes's ontology.

Aristotle's rule of proportions of the factors of motion, presented in VII 5 of the Physics, characterizes Aristotelian force. Observing that the locomotion to which Aristotle applied the Rule is the motion produced by manual labor, I develop an interpretation of the factors of motion that reveals that Aristotelian force is Newtonian power. An alternate interpretation of the Rule by Toulmin and Goodfield implicitly identifies Aristotelian force with Newtonian force. In order to account for the absence of an acceleration in the rate of forced motion, they incorporate into the Rule the medium's resistance to motion due to viscosity as an additional factor. The resulting interpretations of the original factors of motion lose the exactness the power interpretation grants them. The constant rate of forced motion follows immediately from the power interpretation. It is also compatible with the Rule's description of the motion that is produced by the sum of forces.

This paper examines Descartes' problematic relational theory of motion, especially when viewed within the context of his dynamics, the Cartesian natural laws. The work of various commentators on Cartesian motion is also surveyed, with particular emphasis placed upon the recent important texts of Garber and Des Chene. In contrast to the methodology of most previous interpretations, however, this essay employs a modern "spacetime" approach to the problem. By this means, the role of dynamics in Descartes' theory, which has often been neglected in favor of kinematic factors, is shown to be central to finding a solution to the puzzle of Cartesian motion.

This paper is the second of a two-part reexamination of causation in Descartes's physics. Some prominent contemporary scholars, including Gary Hatfield and Daniel Garber, have argued that Descartes is an Occasionalist about natural motion. On their reading, Descartes holds that God alone causes the motions that are not caused by the free actions of finite minds. Hatfield and Garber offer similar, but independent arguments that Descartes's views about physics – in particular, his arguments that the laws of nature are grounded in God's immutability – entail Occasionalism about natural motion. In this paper I argue contra Hatfield and Garber that Descartes's natural philosophy does not entail Occasionalism. Descartes holds that God is a direct efficient cause of every natural motion. Yet he does not take this to imply that bodies lack genuine causal powers. According to Descartes, God concurs with bodies to cause natural motion in such a way that both God and bodies are genuine, efficient causes of motion. I conclude by presenting an account of how Descartes's theory of body is compatible with the thesis that bodies have intrinsic active causal powers.

This essay explores two of the more neglected hypotheses that comprise, or supplement, Descartes’ relationalist doctrine of bodily motion. These criteria are of great importance, for they would appear to challenge Descartes’ principal judgment that motion is a purely reciprocal change of a body’s contiguous neighborhood. After critiquing the work of the few commentators who have previously examined these forgotten hypotheses, mainly, D. Garber and M. Gueroult, the overall strengths and weaknesses of Descartes’ supplementary criteria will be assessed. Overall, despite their ingenuity, it will be demonstrated that Descartes’ criteria cannot rescue his brand of natural laws from the inherent limitations of his strong relational account of motion.

: Given Descartes's conception of extension, space and body, there are deep problems about how there can be any real motion. The argument here is that in fact Descartes takes motion to be only phenomenal. The paper sets out the problems generated by taking motion to be real, the solution to them found in the Cartesian texts, and an explanation of those texts in which Descartes appears on the contrary to regard motion as real.