In either case, the resulting product exhibits knowledge of its particular niche, be it spectrochemical analysis of magnesium alloy production or capturing insects. There are crucial differences between the linguistic products with which Popper populates World 3 and the instruments with which I am concerned. We should seek true theories, and Popper offers an elaborate theory of verisimilitude as one way to understand error elimination. At the most elementary level, we want our theories to be accurate, true to the objects they claim to describe. It is essential that there be one for evolutionary epistemology to operate, and, hence, for instruments to be expressive.
Propositional knowledge provides material for further theoretical reflection.
In the material world, functions are manipulated. In a spectrograph, photographic film is used to record spectral intensities, which are then read by the analyst. In a direct reader, the function of photographic film is replaced by photo-multiplier tubes. Ian Hacking's concept of a phenomenon, coupled with the instrumentician's purposive interest in the phenomena he or she seeks to develop and deploy, provides the best first analysis of a function. The phenomena that instrument construction requires are dependable regularities in material behavior.