ABSTRACT
The shift from classification by difference to classification by similarity in the two-object Disjoint condition would be explained by the same hypothesis, and this would be the only other supporting evidence for this speculation. Classification by similarity is not only dominant everywhere, but at the youngest age it takes place just in the two ambiguous class conditions, i.e. Additive and Multiplicative, while in the only non-ambiguous class condition, Disjoint, classification is by difference. By 6-9 months of age, children begin to form groups of objects, where-by classification can be studied in both their sequential sorting activity and the products thus generated. In the Multiplicative condition, classification shifts from similarity to difference back again to similarity. In the Additive condition, the passage is from no classification directly to classification by similarity. Only the Disjoint condition conforms to the predicted sequence. It remains true, however, that, over all, classification by difference is more confined and occurs at a comparatively earlier age.
