The general process of establishing whether something (an interaction technique, system, theory, design principle, toolkit) is in some sense 'valid' – correct, true, usable. Within HCI there is often a focus on empirical evaluation of a system, theory or other artefact after it has been created. However, this is effectively impossible for generative artefacts (things that create other things) such as toolkits, methodologies or design principles, and then other methods, such as justification based on reasoning and past literature, become more important.
Defined on page 9
Used on pages 8, 9, 10, 11, 12, 14