[u] Nothing is more common in conversation than for a talker to affirm that such and such a position must be _untrue_ "because it is inconceivable." The assertor ought in return to be asked one or two questions, _e.g._, "Do you mean inconceivable to yourself or to the generality of Mankind?" If the latter, "Is the contradictory also inconceivable?" Again, "Do you mean by the word inconceivable, _unthinkable_ or _unimaginable_?" Few people clearly consider this last distinction. Further, "If unthinkable, is it absolutely so, or only very difficult to think?" And it seems likewise important to deliberate whether any position ought to be pronounced absolutely unthinkable, unless the human mind lies under a stern necessity of thinking and accepting its contradictory. [92] "Conceivable" and other like expressions are always relative to conceiving minds; and what appears either conceivable or inconceivable to one mind, may be the contrary to another. A painter not only conceives,--but draws a Centaur, and places him feeding on a wide plain or sloping hill side. But, can the Physiologist conceive such a monstrosity? The solution is easy; the painter thinks of his figure, the physiologist of the structure; and this example furnishes a good caution as to the use of similar words. From words we may pass to ideas. Take any conception involving the condition of Time or Space,--(those two optical tubes of our mind's perceiving eye),--and place it before the understanding; first as a _Finite_ and next as an _Infinite_. The result is a conflict of arguments, ending in a contradiction of all possibility that _either_ way the conception can be true. Any one moderately acquainted with Kant's best-known work, is aware that, by thus treating the world's existence, he raises overwhelming difficulties against its being _either_ limited or unlimited in extent;--eternal _or_ having a commencement in duration;--(p. 338. Ed. Rosenkranz) yet, the world _does_ exist in fact. Kant goes on to subject other cosmological ideas to the same enigmatical reasoning, with the same consequences. Some readers of purely modern science, may illustrate this question of the "_conceivable_" by what has been written on that extraordinary riddle, the "_four_ dimensions of space." They will see opinions _pro_ and _con_ in an article by Professor Sylvester in Nature vol. 1. A note (p. 238) contains one conclusion of the Professor's, interesting as _his_ answer to a question asked by us a few paragraphs back. He says, "If an Aristotle, or Descartes, or Kant assures me that he recognises God in the conscience, I accuse my own blindness if I fail to see with him.... I acknowledge two separate sources of authority,--the collective sense of mankind, and the illumination of privileged intellects." Plato then may have really _seen_ more than Lucretius--Coleridge more than Comte or Littré.