Many definitions of mind and thinking have been given. Iknow of but one that goes to the heart of the matter: response to the doubtful as such. No inanimate thing reacts to things as problematic. Its behavior to other things is capable of description in terms of what is determinately there. Under given conditions, it just reacts or does not react. Its reactions merely enstate anew set of conditions, in which reactions con- tinue without regard to the nature of their outcome. It makes no difference, so to say, to astone what are the results of its interactions with other things. It enjoys the advantage that it makes no difference how it reacts, even if the effect is its own pulverization. It requires no argument to show that the case is different with aliving organism. To live signifies that a connected continuity of acts is effected in which preceding ones prepare the conditions under which later ones occur. There is achain of cause and effects, of course, in what happens with inanimate things. But for living creatures, the chain has a particular cumulative continuity, or else death ensues.