Based on research into development contract practices and the interpretation of the verb `shall', recommendations are made for the use of legal style in engineering design specifications. The choice of style formality affects a contracting party's negotiating position in the event of disputes and also the communication effectiveness of the specification. Factors to be considered in the choice include: marketplace norms, influenced by the buyer-seller relations; organizational norms, influenced by the nature of the organization and the levels of technology and complexity of its products; and specification-writer norms, influenced by previous experience and notions of professionalism. Recommendations are made for both engineering managers and communication teachers.