So what's proposed is a sort of foundationalism . The semantics of observation concepts is indeed special: First, in that--given an intact observer--the nomologically sufficient and semantically relevant conditions for their tokenings are specifiable 'purely externally'; viz., purely psychophysically . And second, in that all the other semantically relevant symbol/world linkages run via the tokening of observation cuncepts . 'Horse' means horse if 'horse' tokenings are reliably caused by tokenings of psychophysical concepts that are in turn caused by instantiations of psychophysical properties for which instantiations of horse are in fact causally responsible. The causal chain runs from horses in the world to horsy looks in the world to psychophysical concepts in the belief box to 'horse' in the belief box. 'Horse' means horse because that chain is reliable.