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.