We suggest that HCI designs characteristically embody multiple, distinct psychological claims, that virtually every aspect of a system's usability is over determined by independent psychological rationales inherent in its design. These myriad claims cohere in being implemented together in a running system. Thus, HCI artifacts themselves are perhaps the most effective medium for theory development in HCI. We advance a framework for articulating the psychological claims embodied by artifacts. This proposal reconciles the contrasting perspectives of theory-based design and hermeneutics, and clarifies the apparent paradox of HCI application leading HCI theory. © 1989 ACM.