To determine to what extent children of preschool age comprehend the meaning of logical connectives, 64 5- and 6-year-olds were told to hand differently colored and shaped wooden blocks to an experimenter. The commands involved various English idioms used for conjunction (e.g. both black and round), disjunction (either black or round), and negation (not round). Analysis of the results indicated that socioeconomic status was the most telling factor, with disadvantaged children performing poorest. In addition, the older children performed better than the younger ones, but sex differences were not significant. The data further showed that disjunction was by far the most difficult operation for children and that the idiom in which the concept was expressed was a significant factor. A predictive regression model was developed from the data. A second experiment was performed with 112 4- to 6-year-olds. This experiment was modeled after the first except that type of connective, type of idiom, and order of commands were varied. The type of connective had the greatest effect but negation was also an important variable. (MH)