Observed material is necessary to suggest ideas and it is equally necessary to test them. The senses are, existentially speaking, the organs by which we obtain the material of observation. But, as we have previously noted, this material is significant and effective for purposes of knowing only as it is connected with operations of which it is the product. Merely physical interactions, whether of external things or of the organism, yield observations that form the material of inquiry} aprob- lematic material. Only operations intentionally performed and attentively noted in connection with their products give ob- served material apositive intellectual value, and this condi- tion is satisfied only by thought: ideas are the perception of this connection.