ON MATTER AND FOKCE. 3 



perfect knowledge which is based upon reason 

 and demonstration, and not on external or 

 internal authority. 



In this lecture, I intend to bring before you 

 the history of our ideas regarding the union of 

 ponderable matter and force in those sciences 

 into which the idea of life does not enter. 



Three distinct stages of ideas or epochs of 

 thought may be clearly recognised. 



The first may be considered as the authori- 

 tative stage, or that of complete separation 

 between the ideas of ponderable matter and 

 force. This stage may be summed up in two 

 words, materialism, and immaterialism or 

 spiritualism. It may be called primitive, 

 because it implies a state of almost complete 

 ignorance of the first principles of natural 

 knowledge. 



The second stage is founded partly on 

 authority and partly on natural knowledge. It 

 is marked by the incomplete separation between 

 the ideas of ponderable matter and force. Force 

 is held to be imponderable matter, or to be 

 inseparably united with imponderable matter. 

 This may be called the stage of imponderable 



