13^ ^^' Percival on the 



Speculations on the Perceptive Power of 

 Vegetables. By Thomas Percival, M. D. 

 F. R. S. i^c. &c. Read February i8, 1784. 



- - - - Thefe are not idle, philofophic dreams; 

 Full Nature teems with life. - - - - 



TaoiisoK's Spring, Second Edit. line 136.* 



T N all our enquiries into truth, whether natural 

 "■■ or moral, it is necefiary to take into previous 

 confideration, the kind of evidence which the 

 fubjefl admits of j and the degree of it, which 

 is fufRcient to afford fatisfaftion to the mind. 

 Demonftrative evidence is abfolute, and without 

 gradation; but probable evidence afcends, by 

 regular fteps, from the lowed prcfumption, to 

 the higheft moral certainty, A fingle prefump- 

 tion is, indeed, of little weight; but a feries 

 of fuch imperfect proofs may produce the fulleft 

 convidlion. The ftrength of belief, however, 

 may often be greater, than is proportionate to 

 the force and number of thefe proofs, either 

 individually or colledively confidered. For, 

 as uncertainty is always painful to the under- 

 flanding, very flight evidence, if the fubjedl 



* Thefe lines are omitted in the fubfequent editions of 

 Thomfon's ^eafons. 



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