ii6 THE GRAMMAR OF SCIENCE 



a cell. The difference between the two branches of 

 science is rather quantitative than qualitative ; that is, 

 the descriptions of mechanics are simpler and more 

 general than those of biology. So wide-embracing and 

 general are the laws of motion, so completely do they 

 describe our past experience of many forms of change, 

 that with a considerable degree of confidence we believe 

 they will be found to describe all forms of change. It is 

 not a question of reducing the universe to a " dead 

 mechanism," but of measuring the amount of probability 

 that one description of change of a highly generalised 

 and simple kind will ultimately be recognised as capable 

 of replacing another description of a more specialised and 

 complex character. It is not taking biology out of one 

 branch of what might be termed descriptive science and 

 removing it into another — that of prescriptive science. 

 Here by prescriptive science I denote an imaginary aspect 

 of science, which mechanics are too frequently supposed 

 to present, namely, that of deducing some inherent 

 necessity in the routine of perceptions, instead of merely 

 describing that routine in simple statements. When, 

 therefore, we say that we have reached a " mechanical 

 explanation " of any group of phenomena, we only mean 

 that we have described in the concise language of 

 mechanics a certain routine of perceptions. We are 

 neither able to explain why sense-impressions have a 

 definite sequence, nor to assert that there is really an 

 element of necessity in the phenomena. Regarded from 

 this standpoint the laws of mechanics are seen to be 

 essentially an intellectual product, and it appears absolutely 

 unreasonable to contrast the mechanical with the intel- 

 lectual when once these words are defined in an accurate 

 manner. 



§ 2. — Force as a Cause 



If force be looked upon as the cause of change, in the 

 sense that it necessitates a certain routine of perceptions, 

 then we have no means of dealing with force. It may be 

 the structure of the perceptive faculty, or it may be any of 



