148 
The Inconceivable as a Test of Truth. [March, 
barbarous, who are completely human beings and not idiots. 
Idiots are persons incapable of perceiving that it is impos- 
sible that two contradictions should be either both true or 
both false : I take to be persons either without the faculty 
of reason or with the means of communication so deranged 
that we may imagine them to mean one thing when they 
seem to say or signify another, while we cannot determine 
that they conceive any idea at all. I would now define 
“ the inconceivable” to be that which no one in possession of 
reason can entertain for a moment as possible, but must 
rejeCt as repugnant to reason itself, as a contradiction which 
destroys itself, in which there is nothing to picture to the 
mind or to discuss “ vox ct prceterea nihil” If this be so, 
whatever was at any time inconceivable will be for ever so, 
and nothing that has ever been conceived was at any period 
or by any other persons inconceivable. What men could be 
persuaded to believe, or even to entertain as possible or 
probable, has always varied with the circumstance and 
will always vary ; but before these questions of possibility, 
probability, or credibility can arise, the mind must first be 
able to conceive the proposition, that it does not in the ex- 
pression destroy itself. It must stand before the mind as 
possible under some circumstances, even if it is to be con- 
demned as impossible under the existing or supposed cir- 
cumstances. The ancients, who are erroneously said to have 
been unable to conceive the existence of Antipodes, because 
they refused to believe it, had their attention been drawn to 
some flies walking on the ceiling, just as others walked upon 
the table, would have replied that men were not like flies, 
a direCt appeal to experience. They conceived the proposi- 
tion, but they rejected it on account of certain objections. 
The same is true of other ordinary illustrations of the “ in- 
conceivable.” But we have here the means of giving a 
clear definition of it, and thus restoring the term to useful- 
ness. The man who can comprehend the general proposi- 
tion, that of two contradictions both cannot possibly be true, 
nor both false, anywhere or in any state of being, is pos- 
sessed of reason. The man who cannot comprehend this as 
a general proposition is destitute of reason. “The incon- 
ceivable” is that which every man possessed of reason is ipso 
facto compelled to rejeCt as incapable of being presented to 
the mind as a supposition, as involving the negation of that 
understanding which was to consider it as in faCt self de- 
structive. It is on this ground, and on this ground only , 
that Sir W. Hamilton can affirm his two proposition, that 
their contradictories are to this exaCt extent absurd. To say, 
