iv INTRODUCTION. 



Nature in making plants and animals can but use such material sub- 

 stances as exist. Now these substances have many properties. Suppose 

 then that Nature has selected one or more of them for a given purpose, 

 in virtue of their having this or that suitable property ; she must take 

 them not only with this desirable property, but with all their other 

 characters, whatsoever these may be ; and these other properties, which 

 were not the cause of the selection, will afterwards assert themselves, 

 and give rise to necessary consequences not included in her design. 

 Thus " we must not expect to find everything in the body made for a 



I purpose. Its parts are mostly the result of final causes ; but their 

 material constitution entails as necessary consequences much that is 

 incidental and undesigned."^ These incidental and unforeseen results 

 may be perfectly useless,^ nay, may even sometimes be baneful;' but, 

 on the other hand, they may be laid hold of by Nature, and incorporated 

 in her scheme, though not originally included within it.* The excreta, 

 for instance, are the result of necessity ; for the body wears away, and 

 the products of its decay, together with the surplus and the indigestible 

 parts of the food, must necessarily be eliminated. But these excreta 

 are in many cases utilised, and converted into means of defence.' Or, 

 to give another example ; the formation of the skin is the necessary 

 consequence of the exposure of the external surface to friction and 

 evaporation,* and the growth of hair upon the scalp is the necessary 

 and incidental consequence of certain arrangements in the skull, which 

 were intended by Nature to answer another purpose.'' But this skin 

 when once formed, and this growth though undesigned, are utilised 

 by Nature, and turned to account in furnishing a protection to the parts 

 beneath against excess of heat or cold. In other words, then. Nature 

 does the best she can with the materials that are at hand ; but the 

 I properties of those materials are beyond her control, and such con- 

 sequences as follow upon those properties are the results of necessity.* 



^ D, P. iv. 2, 8. So also De Anima, iii. 12, 2 : " Everything given by Nature is either 

 itself given for an end, or is the incidental accompaniment of something else which is 

 given for an end." 



^ Those characters of an organism, says A. (D^ Gen. v. i.) that are essential, that is, 

 that form part of its natural design, are fixed and immutable ; those that are unessential, 

 casual, and outside the plan, are variable. Thus, an eye is essential to an animal that is 

 intended by Nature to see, and is invariably present in such ; but the precise colour of the 

 eye is, speaking generally, unessential, and therefore variable, being left to the imcontrolled 

 action of material causes. 



' D. P. iii. 2, 19. 



* D. P. iii. 2, 15. "The necessary results of existing material conditions are made 

 available by rational nature for a final cause." 



* Cf. iii. 2, note 8. « D. G. ii. 6, 26. ' D. P. ii. 14, 6, and ii. 7, 19. 



' " Magnopere hallucinantur, quicumque eas (Jina/ causes) physicis causis adversari aut 

 repugnare putent. Nam causa reddita, quod palpebrarum pili oculos muniant, nequicquam 

 repugnat altera ilia, quod pilositas soleat contingere humiditatum orificiis. Neque causa 

 reddita, quod coriorum in animalibus firmitudo pertinet ad cceli injurias prepulsandas, 

 adversatur illi alter!, quod ilia firmitudo fit ob contractionem pororum in extimis corporum 

 per frigus et depraxlationem aeris, etc." — Bacons De Augin. Sclent, iii. 4. 



