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tion of the senses, the motions of the imagination, appetite, 

 and will, the motion of mind, the determination, and other 

 intellectual faculties they have their own proper doctrines 

 under which we range them, confining the whole of physics 

 to matter and efficient, and assigning over forms and ends 

 to metaphysics. 



We must annex two remarkable appendages to physics, 

 with regard rather to the manner, than the matter of in 

 quiry; viz., natural problems, and the opinions of the an 

 cient philosophers. The first is an appendage of nature at 

 large, and the other of nature united or summed up ; both re 

 lating to a diligent kind of doubting, which is no contemp 

 tible part of knowledge. Now, problems contain particular 

 doubts and opinions, general ones, as to principles and 

 structure. In the books of Aristotle we have a noble 

 example of problems, deserving not only the praises but 

 the imitation of posterity, since new doubts are daily aris 

 ing. But the utmost caution is to be used in such an un 

 dertaking. The recording and proposing of doubts has two 

 advantages; the one, as it defends philosophy against errors, 

 when that which is not clear is neither judged nor asserted, 

 lest error thus should multiply error, but judgment is sus 

 pended upon it, and not made positive; the other is, that 

 doubts once registered are like so many sponges, which 

 perpetually suck and draw to themselves the increases of 

 knowledge; whence those things which would have been 

 slightly passed over, unless they had been doubted of be 

 fore, come now from this very doubting to be more atten 

 tively considered. But these two advantages will scarce 

 balance this single inconvenience, unless well provided 

 against; viz., that when a doubt is once admitted for 

 just, and becomes, as it were, authentic, it presently 

 raises up disputants on both sides, who transmit to pos 

 terity the same liberty of doubting still ; so that men seem 

 to apply their wits rather to nourish the doubt than solve 

 it. And of this we everywhere meet with examples in law 

 yers and scholars; who, when a doubt once gains admit- 



