SCIENTIFIC METHOD AND SEMANTICS
The concept of causality has a natural basis in simple experience: things are moved around either by other things or by human agency. The anthropomorphic character of the customary conception of causality has often been noted; it suggests the view that all the things in the world are mutually connected by little strings, or the world as a puppet show. This string model of causality is often employed in every-day life and re-appears, in an improved version, in the simplest interpretation which is sometimes given to Newtonian mechanics. We have particles, and forces act between them: force is considered as a cause since it produces a change. The particle-force model of this naive kind is often said to express the mechanistic view of the world.
The identification of force and cause has led to what is commonly called 'dynamical causality'. In spite of its obvious faults it is a step towards a better understanding of how physical events are related to one another. It is true that the obscurity of the concept of force, and its connexion with human effort, is objectionable. As Poincaré remarked: 'Quand on dit que la force est la cause d'un mouvement, on fait de la metaphysique'. But the use of the term 'force' at least allows us to speak about causal relations within the context of a definite theory and to discuss specific laws. For Newton's second law takes forces as the accelerations of mass particles, and all change is expressed in terms of the coördinates of space and time. Causality is then the relation between two events described by a differential equation of the second order which, moreover, does not contain explicit functions of the time. The precise mathematical formulation of the laws of mechanics permits us to correlate two events by an invariable relationship: if we know the law of force, the values of position and momentum of a particle at any given time are determined through the differential equation, provided we know the initial and the boundary conditions of the problem.