Will and Guidance 161 



with the material world is impossible, in 

 spite of their clamorous experience to the 

 contrary (or else, on the strength of that 

 experience, to conceive that there is some- 

 thing the matter with the formulation of 

 physical and dynamical laws), is because all 

 such interference is naturally and necessarily 

 excluded from scientific methods and 

 treatises. 



In pure Mechanics, " force " is treated as 

 a function of configuration and momentum : 

 the positions, the velocities, and the accelera- 

 tions of a conservative system depend solely 

 on each other, on initial conditions, and on 

 mass ; or, if we choose so to express it, the 

 co-ordinates, the momenta, and the kinetic 

 energies, of the parts of any dynamical 

 system whatever, are all functions of time 

 and of each other, and of nothing else. In 

 other words, we have to deal, in this mode of 

 regarding things, with a definite and com- 

 pletely determinate world, to which pre- 

 diction may confidently be applied. 



But this determinateness is got by refusing 



II 



