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Laws of Nature

Laws of Nature. The Ramsey-Lewis Theory. Review. For all P, P is a law of nature iff . The Regularity Theory : For all P, P is a law of nature iff P is a contingently true generalization. Objection #1 : Restricted Generalizations Objection #2 : Vacuous Generalizations

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Laws of Nature

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  1. Laws of Nature The Ramsey-Lewis Theory

  2. Review • For all P, P is a law of nature iff . • The Regularity Theory: For all P, P is a law of nature iff P is a contingently true generalization. • Objection #1: Restricted Generalizations • Objection #2: Vacuous Generalizations • Objection #3: Accidental Generalizations

  3. Deductive Systems • The Revised Regularity Theory: For all P, P is a law of nature iff P is a contingently true generalization that . • A deductive system is a collection of axioms, together with rules of inference. • A theorem is any statement that follows from the axioms by the rules of inference.

  4. Euclidean Geometry • Any two points can be joined by a straight line. • Any straight line segment can be extended indefinitely in a straight line. • Given any straight line segment, a circle can be drawn having the segment as radius and one endpoint as center. • All right angles are congruent. • Parallel postulate.

  5. Newtonian Mechanics • First Law: A body at rest remains at rest, and a body in motion continues to move in a straight line with a constant speed unless and until an external unbalanced force acts upon it. • Second Law: The rate of change of momentum of a body is directly proportional to the impressed force and takes place in the direction in which the force acts. • Third Law: Whenever A exerts a force on B, B is simultaneously exerting a force of the same magnitude on A, in the opposite direction.

  6. Deductive Systems • How many axioms are there? How complicated are they? • How interesting are the theorems? How applicable are they? • The best deductive system is the one that achieves the best balance of simplicity and strength.

  7. The Ramsey-Lewis Theory • The Ramsey-Lewis Theory: For all P, P is a law of nature iff P is a contingently true generalization that belongs to the best deductive system. • Objection #1: Restricted Generalizations • All the objects in this room exert a force on each other inversely proportional to the square of the distance between them.

  8. The Ramsey-Lewis Theory • The Ramsey-Lewis Theory: For all P, P is a law of nature iff P is a contingently true generalization that belongs to the best deductive system (as an axiom or a theorem). • Objection #1: Restricted Generalizations • All the objects in this room exert a force on each other inversely proportional to the square of the distance between them.

  9. The Ramsey-Lewis Theory • The Ramsey-Lewis Theory: For all P, P is a law of nature iff P is a contingently true generalization that belongs to the best deductive system. • Objection #2: Vacuous Generalizations • All plaid panda weigh exactly five kilograms.

  10. The Ramsey-Lewis Theory • The Ramsey-Lewis Theory: For all P, P is a law of nature iff P is a contingently true generalization that belongs to the best deductive system. • Objection #3: Accidental Generalizations • All gold spheres are less than a mile in diameter. • All uranium spheres are less than a mile in diameter.

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