There still remain the requirements of reasoning, of calculation, of adaptation to the properties of matter. But, we repeat, this determinism has several possible forms--one can reach the same goal through different means. Besides, these determining conditions are not lacking in any type of imagination; there is only a difference as between lesser and greater. Every imaginative construction from the moment that it is little more than a group of fancies, a spectral image haunting a dreamer's brain, must take on a body, submit to external conditions on which it depends, and which materialize it somewhat. In this respect, architecture is an excellent example. It is classed among the fine arts; but it is subject to so many limitations that its process of invention strongly resembles technical and mechanical creations. Thus it has been possible to say that "Architecture is the least personal of all the arts." "Before being an art it is an industry in the sense that it has nearly always a useful end that is imposed on it and rules its manifestations. Whatever it builds--a temple, a theater, a palace--it must before all else subordinate its work to the end assigned to it in advance. This is not all:--it must take account of materials, climate, soil, location, habits--of all things that may require much skill, tact, calculation, which, however, do not interest art as such, and do not permit architecture to manifest its purely esthetic qualities."[129] Thus, at bottom, there is an identity of nature between the constructive imagination of the mechanic and that of the artist: the difference is only in the end, the means, and the conditions. The formula, _Ars homo additus naturae_, has been too often restricted to esthetics--it should comprehend everything artificial. Esthetes, doubtless, hold that their imagination has for them a loftier quality--a disputed question that psychology need not discuss; for it, the essential mechanism is the same in the two cases: a great mechanic is a poet in his own way, because he makes instruments imitating life. "Those constructions that at other times are the marvel of the ignorant crowd deserve the admiration of the reflecting:--Something of the power that has organized matter seems to have passed into combinations in which nature is imitated or surpassed. Our machines, so varied in form and in function, are the representatives of a new kingdom intermediate between senseless and animate forms, having the passivity of the former and the activity of the latter, and exploiting everything for our sake. They are counterfeits of animate beings, capable of giving inert substances a regular functioning. Their skeleton of iron, organs of steel, muscles of leather, soul of fire, panting or smoking breath, rhythm of movement--sometimes even the shrill or plaintive cries expressing effort or simulating pain:--all that contributes to give them a fantastic likeness to life--a specter and dream of inorganic life."[130]