This study argues that including aspects of user experience relevant to the user's knowledge of a product's context-of-use in the early stages of product design can enhance the design of product usability. To explore these issues, research was undertaken to respond to three research questions: (i) What aspects of user experience influence people's understanding of product usability? (ii) What is the nature of the differences between users' and designers' understandings of product usability? (iii) How can context-of-use and human experience enhance the design of product usability? Findings from the study have shown that experience, context-of-use and knowledge about a product's usability are interrelated. Conceptual principles and design principles were established based on findings to explain (i) the relationships between aspects of experience and areas of product usability and (ii) differences between designers' and users' concepts of product usability. These principles responded to the first two research questions. Causal relationships found between experience and product usability suggested the need to implement them in an accessible manner for a product design process. A design tool -- named the Experience and Context Enquiry Design Tool (ECEDT) -- was devised to exemplify the implementation of findings. A trial run verified that the type of information that ECEDT brings to designers could assist them to address usability and experience issues during the early stages of the design process. This result responded to the third research question of the study. This study's conceptual principles and design principles contribute new knowledge to design theory and practice. This knowledge contributes to design theory in providing greater detail about the differences between designers and users than that addressed by existing theory; it contributes to design practice as it informs designers about the aspects of human experience that prompt users' understanding of a product's use. In doing so, it can potentially assist in the design of products that embed new technological applications, and support the design of product usability.