28. It should be recollected that there must be some system which is the most complete of all systems, some planet which is the largest of all planets. And if that largest planet, in the most complete system, be, after being for ages tenanted by irrational creatures, at last, and alone of all, occupied by a rational race, that race must necessarily have the power of asking such questions as these: Why they should be alone rational? Why their planet should be alone thus favored? If the case be ours, we may hope to be then able to answer these questions, when we can explain the most certain fact which they involve; Why the Earth was occupied so long by irrational creatures, before the rational race was placed upon it? The mere power of asking such questions can prove or disprove nothing; for it is a power which must equally subsist, whether the human inhabitants of the earth be or be not the only rational population which the universe contains. If there be a race thus favored by the Creator, they must, at that stage of their knowledge in which man now is, be able to doubt, as man does, of the extent and greatness of the privilege which they enjoy. 29. The argument that the Fixed Stars are like the Sun, and therefore the centres of inhabited systems as the Sun is, is sometimes called an argument from Analogy; and this word _Analogy_ is urged, as giving great force to the reasoning. But it must be recollected, that precisely the point in question is, whether there _is_ an analogy. The stars, it is said, are like the Sun. In what respects? We know of none, except in being self-luminous; and this they have in common with the nebulæ, which, as we have seen, are not centres of inhabited systems. Nor does this quality of being self-luminous at all determine the degree of condensation of a star. Sirius may be less than a hundredth or a thousandth of the density of the Sun. But the Stars, it may be further urged, are like the Sun in turning on their axes. To this we reply, that we know this only of those stars in which, the very phenomenon which proves their revolution, proves also that they are unlike the Sun, in having one side darker than the other. Add to which, their revolution is not connected with the existence of planets, still less of inhabitants of planets, in any intelligible manner. The resemblance, therefore, so far as it bears upon the question, is confined to one single point, in the highest degree ambiguous and inconclusive; and any argument drawn from this one point of resemblance, has little claim to be termed an argument from analogy.[21]