'Material thing' is a two-level concept. In 'first-order extension' - the field of perceptual experience - it is a 'body' that may 'body forth' (show, express) a 'content', like the bodies of persons or pictures. In 'second-order extension' -the physical field or space - it is a 'physical object' whose micro-constitution is the target of the reference of theoretical terms or formulae. As such, it has no content - nothing to 'express'. In the description of a material thing in first-order (...) extension, terms are used whose reference is fixed by ostension. (The picture's pigment is cracked, the person's eyes are blue.) The reference of theoretical terms - to the material thing in second-order extension - is fixed by their interrelationships in the theory. (shrink)