(noun) the actualization of form-giving cause as contrasted with potential existence / (noun) a hypothetical agency not demonstrable by scientific methods that in some vitalist doctrines is considered an inherent regulating and directing force in the development and functioning of an organism (from Aristotelian metaphysics)
these are the attributes of men who are now American through and through, an impossiblity, no matter how you look at it, an act of the will, an entelechy that neither Melville nor Twain consciously constructs