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
 Objection #3: Accidental Generalizations
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.
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.
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.
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.
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.
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.
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.
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.