These three cases have been purposely selected so as to form a series from the more rudimentary to more complicated cases of reflection. The first illustrates the kind of thinking done by every one during the day's business, in which neither the data, nor the ways of dealing with them, take one outside the limits of everyday experience. The last furnishes a case in which neither problem nor mode of solution would have been likely to occur except to one with some prior scientific training. The second case forms a natural transition; its materials lie well within the bounds of everyday, unspecialized experience; but the problem, instead of being directly involved in the person's business, arises indirectly out of his activity, and accordingly appeals to a somewhat theoretic and impartial interest. We shall deal, in a later chapter, with the evolution of abstract thinking out of that which is relatively practical and direct; here we are concerned only with the common elements found in all the types. [Sidenote: Five distinct steps in reflection] Upon examination, each instance reveals, more or less clearly, five logically distinct steps: (_i_) a felt difficulty; (_ii_) its location and definition; (_iii_) suggestion of possible solution; (_iv_) development by reasoning of the bearings of the suggestion; (_v_) further observation and experiment leading to its acceptance or rejection; that is, the conclusion of belief or disbelief. [Sidenote: 1. The occurrence of a difficulty] [Sidenote: (_a_) in the lack of adaptation of means to end] 1. The first and second steps frequently fuse into one. The difficulty may be felt with sufficient definiteness as to set the mind at once speculating upon its probable solution, or an undefined uneasiness and shock may come first, leading only later to definite attempt to find out what is the matter. Whether the two steps are distinct or blended, there is the factor emphasized in our original account of reflection--_viz._ the perplexity or problem. In the first of the three cases cited, the difficulty resides in the conflict between conditions at hand and a desired and intended result, between an end and the means for reaching it. The purpose of keeping an engagement at a certain time, and the existing hour taken in connection with the location, are not congruous. The object of thinking is to introduce congruity between the two. The given conditions cannot themselves be altered; time will not go backward nor will the distance between 16th Street and 124th Street shorten itself. The problem is _the discovery of intervening terms which when inserted between the remoter end and the given means will harmonize them with each other_. [Sidenote: (_b_) in identifying the character of an object]