Causality 03: The Modern "Epistemic Turn" and Causality

Transcription

1 Causality 03: The Modern "Epistemic Turn" and Causality Announcement Register to BEEF! Reading assignment J.L. Macke, Causes and Conditions, excerpt (the first 3 pages) PDF in Readings From Medieval to Modern physics Impetus theory Natural / violent motion -> assumption of the nature" Transference of impetus" Moving principle is found in each body Galileo s new science No natural/violent distinction Motion is purely relational The principle of inertia Galileo Galilei ( ) Galilean Invariance Ship experiment drop a stone from on top of the mast and observe where on the deck it lands whether the ship is moving (at constant velocity) or in still does not matter

2 Likewise for the Earth whether it is orbiting around the sun or in still does not matter to motion on the earth Motion is relative: change in distance from the surrounding objects (frame) Inertia: the new principle Galileo: A body moving on a level surface will continue in the same direction at a con stant speed unless disturbed c.f. alileoinertia.html Descartes: Principia Philosophiae, Pt. II, 37 "The first law of nature: each thing when left to itself continues in the same st ate; so any moving body goes on moving until something stops it." For Descartes texts see: Newton: Philosophiae Naturalis Principia Mathematica Law 1: Every body preservers in its state of rest, or of uniform motion in a right line, unless it is compelled to change that state by forces impressed thereon." Epistemological & metaphysical implications Shift in explanandum Aristotle - medieval physics: Motion (= change in location) Modern physics: Change in motion (= acceleration) Body is inert it does not have moving power -> no need for essence body as a passive matter so what is it like? Descartes metaphysics

3 René Descartes ( ) Dualism Res cogitans: mind, soul. Thinking things. Res extensa: bodies, whose essence consists of physical extension. Material substance as pure extension Secondary properties (hardness, color, etc.) are subjective and do not belong to bodies themselves "The nature of body consists just in extension not in weight, hardness, colour or the like." (Principia, II, 4) Mathematics as the means to study the physical world "Geometry and pure mathematics provide me with the only principles I need i n my physics, and the only ones I ll accept. They explain all natural phenome na, and provide us with quite certain demonstrations regarding them (Principia, II, 64) Descartes on causation Formal & Material causes (Principia, II, 23) "All the variety in matter, all the different forms it takes, depend on motion." -> difference in substantial form & material is also reduced to motion Final causes (Principia, I, 28) Can we ever know final causes of things? "We ll never explain natural things in terms of the purposes that God or natur e may have had when creating them,

4 and we shall entirely banish them from our natural science. Why? Because w e shouldn t be so arrogant as to think that we can share in God s plans" If so: It s not the final but the efficient causes of created things that we must investigate. A puzzle about efficient causes in Descartes Do they really cause anything? Efficient causes = transference of communication of motion from one body to another But a body is a purely geometrical extension without any active power the motion of a body is just a mode of its being relative to another Then how can such a passive matter cause motion in another body? God as the cement of the universe (Principia, II, 36) "God is the primary cause of motion; and he always preserves the same quantity of motion in the universe" He is also "the particular cause that produces in an individual piece of matter some motion wh ich it previously lacked. So actually it is God who causes motion. Bodies provide just an occasion. Occasionalism The thesis If A causes B, what actually makes B happen is God. A provides only a cue (occasion). c.f. virtual reality games. Malebranche: there must be a necessary connection between a cause and its effect But such a connection can never be discovered -> only God s will can provide such a connection David Hume ( )

5 Skepticism on induction All ravens are black" <- how do we know it is true? All ravens observed so far were black. So the next one will be black as well" <- Uniformity of nature But how do we prove this? -> Induction is just a habit of our mind Skepticism on causality Causal relationship = necessary connection between a cause and an effect? But we can t find any such necessity or power in the impression of a cause "we never can, by our utmost scrutiny, discover any thing but one event following a nother, without being able to comprehend any force or power by which the cause o perates, or any connexion between it and its supposed effect" All we can observe are: 1. Spatial/temporal contingency a cause and its effect are not distant in time and place 2. Temporal succession an effect follows its cause

6 3. Constant conjunction an effect follows regularly after its cause There is nothing more to causal relationships! "we may define a cause to be an object, followed by another, and where all the obje cts similar to the first are followed by objects similar to the second. " From Aristotle to Hume: Summary Three aspects of causality 1. Metaphysics (What is that?) 2. Sematic (What does it mean?) 3. Epistemology (How do we know it?) Aristotle s doctrine/arguments of four causes Semantic -> Metaphysics There are four different senses of explaining why -> four different ways or actions of cause These causal actions are based on his metaphysics & physics The Modern epistemic turn" Descartes, Discourse on Method: "The first [rule] was never to accept anything for true which I did not clearly know to be such ; that is to say,... to comprise nothing more in my judgment than what was presented to my mi nd so clearly and distinctly as to exclude all ground of doubt" Modern skepticism on causality Epistemology -> Metaphysics Descartes: can t know final causes -> better not ask Occasionalists: can t find efficient causal power -> maybe in God Hume: can t find causal power or necessity -> there s no such thing But note... Behind this epistemic turn was the paradigmatic shift in the metaphysical world view. Aristotelian essence physics -> Galilean inertial physics This shift made the notion of cause metaphysically doubtful epistemologically unattainable