A study of children's acquisition of the auxiliary verb system in English is reported. The first section describes the operation of the auxiliary system, and proposes that the behavior of auxiliaries is so complicated that if children were to generalize from one auxiliary to another, they would make predictable errors. The second section reviews data from a large corpus of young children's language for evidence of auxiliary errors. From this data, it was determined that inversion errors are the only auxiliary errors made with appreciable frequency. Based on the scarcity of most error types, it is concluded that children acquire most aspects of the auxiliary system conservatively, and that little evidence of a productive learning strategy emerges from this data. Further research on time factors in the acquisition of the various auxiliaries is recommended to complement these findings. (MSE)