An analogy is a type of reasoning, and as such is referred to the logician for more precise definition. His briefest explanation of the term may be stated as the inference of a further degree of resemblance from an observed degree of resemblance; the argument that because the Earth and Mars agree in the common possession of a solid crust, an atmosphere, presence of water, changes of season, the possibilities of rain and snow, and other observed qualities, they will also agree in the further respect of being inhabited. This may serve as an exemplar of the analogical argument in its purest and most developed form; but in the survey of the varieties and distribution of this natural product of rationality, it will be necessary to include many forms of thought diverging more or less from, though always retaining, a recognizable relation to this type. The analogical inference, indeed, goes back to an inarticulate form, in which it merges into a feeling rather than an argument, a susceptibility to an influence supported by undefined plausibility, rather than a conclusion from tangible evidence. But however lacking in definiteness or formulation, however unconsciously realized and barely expressible, the tendency or disposition to believe is communicated to others and becomes an influential factor in the ultimate fixation of belief and in the guidance of conduct. Logically considered, analogy is always a weak argument; and becomes weaker, as the range of observed resemblance is more and more limited, as the resemblances belong to accidental, unessential traits, and as the underlying basis of the inference is removed from direct verification. Psychologically, its power to influence belief may be very strong, and when this is not the case, there still may exist a disposition to be influenced by analogical considerations, even when these are successfully resisted or suppressed. The instinctive proclivity towards the use of analogies, whether it be logical or anti-logical in effect, forms an interesting psychological trait. Logic counsels how we may think most profitably and correctly; psychology describes how we actually do think or tend to think. The logician is the gardener bent upon training certain selected flowers according to an ideal standard, and eradicating all others as weeds; while the psychologist is the botanist to whom all plants, weeds, and flowers alike are worthy objects of study, and who, indeed, traces significant resemblances between the despised weed and the choice flower.