chap, ix The Divided Labours of the Body 151 



Inference is of two kinds : 



(1) Perceptual, drawn from direct experience, as in 



the inference as to a rain storm from a black 

 cloud. 



(2) Conceptual, which, though based upon experience, 



yet can predict events that have never been 

 experienced. For instance, one who had studied 

 in books only the causes of volcanic activity, 

 might predict with a certain amount of confidence 

 a flow of lava from a volcano, when he saw it in 

 that state of activity which he knew usually pre- 

 ceded an eruption of lava. 

 What we call the emotions, love, hate, fear, and others, 

 are, so far as we can tell, agitations of nervous matter 

 which affect consciousness. Their exciting stimuli — infer- 

 ences for example — proceed, immediately, from within the 

 brain, ultimately, from changes in the outer world. 



We have, therefore, the following orders of conscious- 

 ness, which are easily distinguishable in theory : 



(1) Impressions, or the effects of environmental 



changes upon nervous matter ; the retaining and 

 revival of these constitutes the basis of memory. 



(2) Sensations, which occur when the differences that 



exist between impressions are discriminated. 



(3) Perceptions, which are the outward projections 



into the world, by mental acts, of the molecular 

 disturbances caused in the brain by environ- 

 mental changes. For example, light falls upon 

 the retina, stimulates the optic nerve, and causes 

 a molecular disturbance in the brain, but the 

 consciousness excited in us is not of the brain 

 disturbance, but of the light. 

 It is most essential that the distinction between per- 

 ceptual and conceptual inference be clearly realised, as it is 

 probable that it is the faculty for the latter which more 

 than anything else separates man from the lower animals. 

 We may be nearly certain that many animals exercise per- 

 ceptual inference, and we may affirm with little doubt that 

 none has ever performed a conceptual one. It has been 



