IMMEDIATE INFERENCE. 347 



cases ; for instance, if we discover a new metal, we infer 

 that it will conduct heat and electricity ; and why do we 

 infer this? not so much because some one other metal 

 does so, but chiefly because all the metals we are ac- 

 quainted with do so. But as c all ' may be only a single 

 instance, in some cases from one particular fact we imme- 

 diately infer another ; for example, if we discover that 

 the electric conductivity of selenium is affected by light, 

 we infer that that of tellurium may be also. When we 

 observe a new fact, we not only imagine by inference the 

 existence of other facts of a similar kind, but we some- 

 times further hypothetically infer the existence of a 

 general principle governing them. 



The process of inference has also been divided into 

 immediate and mediate. The former is the simplest, and 

 consists in passing from one idea or proposition to another 

 implied (as in the instances given on page 333) in it. It 

 is based upon the general truth that every positive con- 

 ception has a corresponding negative one ; thus the idea 

 of metals has the complementary negative one of non- 

 metals, which includes every idea (except that of metals) 

 necessary to complete the whole collection of thoughts 

 under consideration at the time ; just as yellow rays and all 

 rays not yellow are complementary to each other, and include 

 all the rays of white light. And when we affirm anything 

 of a positive conception we always imply something respect- 

 ing its negative one, and are thereby enabled to draw an 

 immediate inference concerning the latter ; thus when we 

 affirm that ' all gases are non-conductors of electricity,' we 

 are empowered to infer that ' none of the gases are con- 

 ductors of electricity,' and that ' all conductors of electricity 

 are not gases,' and so on. 



The simplest form of immediate inference is but one 

 step from repetition, and is so simple and obvious that it 



