Reflection thus implies that something is believed in (or disbelieved in), not on its own direct account, but through something else which stands as witness, evidence, proof, voucher, warrant; that is, as _ground of belief_. At one time, rain is actually felt or directly experienced; at another time, we infer that it has rained from the looks of the grass and trees, or that it is going to rain because of the condition of the air or the state of the barometer. At one time, we see a man (or suppose we do) without any intermediary fact; at another time, we are not quite sure what we see, and hunt for accompanying facts that will serve as signs, indications, tokens of what is to be believed. Thinking, for the purposes of this inquiry, is defined accordingly as _that operation in which present facts suggest other facts (or truths) in such a way as to induce belief in the latter upon the ground or warrant of the former_. We do not put beliefs that rest simply on inference on the surest level of assurance. To say "I think so" implies that I do not as yet _know_ so. The inferential belief may later be confirmed and come to stand as sure, but in itself it always has a certain element of supposition. § 3. _Elements in Reflective Thinking_ So much for the description of the more external and obvious aspects of the fact called _thinking_. Further consideration at once reveals certain subprocesses which are involved in every reflective operation. These are: (_a_) a state of perplexity, hesitation, doubt; and (_b_) an act of search or investigation directed toward bringing to light further facts which serve to corroborate or to nullify the suggested belief. [Sidenote: The importance of uncertainty] (_a_) In our illustration, the shock of coolness generated confusion and suspended belief, at least momentarily. Because it was unexpected, it was a shock or an interruption needing to be accounted for, identified, or placed. To say that the abrupt occurrence of the change of temperature constitutes a problem may sound forced and artificial; but if we are willing to extend the meaning of the word _problem_ to whatever--no matter how slight and commonplace in character--perplexes and challenges the mind so that it makes belief at all uncertain, there is a genuine problem or question involved in this experience of sudden change. [Sidenote: and of inquiry in order to test]