Basic to the study of individual differences is the concept of 'general intelligence' or Spearman's g. In this article we suggest that g is largely a reflection of the control functions of the frontal lobe. A series of experiments investigates a phenomenon we call goal neglect: disregard of a task requirement event though it has been understood and remembered. Subjectively it is as though the neglected requirement "slips the subject's mind." Previously described in frontal patients, we show that goal neglect can also be seen in some members of the normal population. In line with conventional distinctions between controlled and automatic processing, eliciting conditions for goal neglect include novelty, weak error feedback, and multiple concurrent task requirements. Under these conditions neglect is linked closely to g and extremely common after frontal lesions. Following many other models, we suggest that behavior in any task is structured by a set of action constraints or requirements, derived in part from verbal instructions and specified at multiple levels of abstraction. A frontal process of constraint or requirement activation is fundamental to Spearman's g.