DE = abcDE,
or D and E never meet but in the absence of A, B, and C.
Fallacies analysed by the Indirect Method.
It has been sufficiently shown, perhaps, that we can by the Indirect Method of Inference extract the whole truth from a series of propositions, and exhibit it anew in any required form of conclusion. But it may also need to be shown by examples that so long as we follow correctly the almost mechanical rules of the method, we cannot fall into any of the fallacies or paralogisms which are often committed in ordinary discussion. Let us take the example of a fallacious argument, previously treated by the Method of Direct Inference (p. [62]),
| Granite is not a sedimentary rock, | (1) |
| Basalt is not a sedimentary rock, | (2) |
and let us ascertain whether any precise conclusion can be drawn concerning the relation of granite and basalt. Taking as before
A = granite,
B = sedimentary rock,
C = basalt,
the premises become
| A = Ab, | (1) |
| C = Cb. | (2) |
Of the eight conceivable combinations of A, B, C, five agree with these conditions, namely