CHARACTER AND LIMITS OF BELIEF AND CERTAINTY. 517 
221. We have appetites, passions, desires, sentiments, clearly defined and readily dis- 
tinguishable from each other. In examining them, we feel that we are examining our- 
selves; that they are portions of ourselves,—different phases, as it were, of the same 
indivisible being. Do we ever doubt their reality? Do we ever feel that we may be mis- 
taken in believing that we love or hate, that we fear or venerate, that we hope or despair? 
You answer, No, emphatically and without hesitation. We know that our own conscious- 
ness can never deceive us, and in that, at least, if nowhere else, may we find a sufficient 
refutation of the skeptical belief that we can be sure of nothing. We know that circum- 
stances cannot affect the reality of our perceptions, that they neither weaken them nor 
exert any control over them. We find, then, in self-consciousness, a second source of posi- 
tive knowledge. 
222. There is still a third source in the apperceptions of reason. We have a faculty 
that furnishes us with abstract ideas,—ideas neither of sense nor of consciousness, although 
they may be first suggested in connection with other truths as the necessary condition of 
those truths. For example, from sense we derive the idea of body, and in connection with 
the idea of body, reason at once suggests the necessary and absolute idea of space. Sense 
discovers the finite, reason mounts to the infinite. Sense perceives the succession of 
phenomena, reason teaches the relation of cause and effect. 
223. These ideas are all essentially distinct, and cannot be confounded with each other. 
We know that body could not exist without space; the finite without the infinite; the 
phenomenon without a cause ; but we can easily conceive of space without body; of the 
infinite without any finite existence; of an efficient cause which has the power in itself of 
either manifesting its efficiency in action, or of remaining entirely at rest. 
224. We know, also, that rational ideas cannot be derived from sense or from self-con- 
sciousness. We can neither see, nor hear, nor feel, nor smell, nor taste space or infinity or 
cause ; nor can we conceive of them as parts of ourselves. And yet we feel and know 
that such ideas are types of actual and necessary existence,—that they represent impor- 
tant truths. 
225. Besides the power of teaching abstract truth, and the kindred power of generaliza- 
tion, reason perceives the necessary relations of different truths, and is capable of lead- 
ing us from the simple to the intricate,—from the clear to the more obscure. These rela- 
tions, when they are plainly perceived, are seen to be unalterable, and founded in the 
necessity of things. Whatever may be the subject of our consideration, we proceed irre- 
sistibly from one conclusion to another, and we feel that from the same data every other 
rational being would have drawn the same inferences. The propositions of Geometry fur- 
nish the most evident proof of this fact, though the proof may be also found in every in- 
