In behavioral science research, language has been increasingly seen to reflect the concepts that the child has acquired prior to, and hence independent of, the acquisition of language. Analyses based on this idea are confined largely to words that denote clear perceptual referents. Language, however, contains many terms that have no portrayable referents. If it is to be meaningful, any search for the contribution of language to thinking should be carried out in the realm where language may have unique properties for organizing experience. Some terms which exemplify, but which far from exhaust, this phenomenon, are found in question words referring to cause (i.e. why), manner (i.e. how) and time (i.e. when). Largely because the question word "why" occurs more frequently and earlier than these other terms the discussion which follows is largely confined to the child's mastery of this term. Data for the first part of the discussion was collected during work with Doris Allen, a linguist who had collected bi-monthly data on the linguistic performance of a middle-class child. The remainder of the discussion deals with data gathered as part of a much broader assessment of the cognitive skills in children of three to six years of age. The materials discussed here specifically concerns a set of 44 items designed to tap the child's ability to deal with problem solving questions. (Author/JM)