The idea behind the concept of 'technology', and of 'technical progress' as a source of growth is simple, isn't it? Many kinds of scientific and technical knowledge are, at least in principle, public goods - once something is discovered, it can be used by anyone - and they can be thought of as growing in a cumulative way - new discoveries are added to what was known before. We are better off than our ancestors primarily because we know more. Economically valuable knowledge unavailable to past generations becomes readily available in reference works, textbooks, and so on. Equipment embodying complex techniques can be bought in the market (computers, software, vehicles, etc.) and people with experience and training can be hired as employees or consultants. There is an element of truth to the idea of a state of technology which changes over time but is available to all at a given date. Some (many) forms of economic knowledge, such as Pat Gunnings 'knowledge of buying and selling opportunities', don't fit this pattern and aren't what we usually mean by 'technology' - which isn't to say they are not important. On closer examination, of course, the simple picture given above dissolves - usable technical knowledge is a mixture of 'public' elements, available to all, with 'private' skills and knowledge peculiar to individuals and organizations, etc. The simple picture still seems to me to have its uses, though. Tony Brewer