12 PHYSICAL EXPEESSION. 



sign) is found with absolute uniformity, whenever 

 the property or function in question is present, we 

 may look upon that physical sign as an absolute 

 proof of the presence of the property. Thus, in 

 a man the power of speech proves the existence 

 of " life ; " physiological knowledge shows that we 

 cannot have speech proceeding from a man unless 

 his body has life. To prove the property life in 

 a human subject it is quite sufficient to prove that 

 he can speak. We do not know what life is in 

 the abstract, but to prove that a man can speak 

 is to prove that he possesses what we call " life." 



It follows, then, that the physical sign " speech " 

 is a criterion of life, or we may say that speech 

 is one expression of life. We see, then, that the 

 uniform coexistence of two phenomena in a subject, 

 of which one is a physical sign, enables us to 

 look upon that physical sign as an expression of 

 the other phenomenon. 



This uniform coexistence may be demonstrated 

 by empirical experience sufficiently extended, and 

 attested by various observers, under varying cir- 

 cumstances. If we analyze the expression of the 

 property " life," given above, we shall learn some- 

 thing further as to why we may speak of " speech " 

 as an expression of life in the subject. It is known 

 that speech is always the result of certain move- 

 ments of the respiratory apparatus, the tongue, and 

 the mouth. Respiration, even when unattended 

 by speech, and when found in animals incapable 

 of speech, is uniformly expressive of the property 

 " life." Further, physiology has shown that active 



