Now: Between Indexical Thoughts and Indexical Thought

It has long been argued that rational action necessitates having indexical thoughts. The ability to understand and generate indexical expressions is also a precondition for interacting in natural language. A rational acting agent that interacts in natural language is, thus, required to develop a proper treatment of indexicality. Treatments of indexicality in the literature have, almost always, assumed an indexical language of thought. I shall argue that, in most common cases, all indexical expressions in said language may be reduced to expressions involving only counterparts of “I” and “now”. I dismiss the language-of-thought “I” as being not indexical at all; this leaves us with “now”. First, I review past approaches to representing and reasoning about “now”, and systematically evaluate them against four criteria which I develop and motivate. Second, I push forward a totally different treatment of “now”, based on a grounded, layered agent architecture. In this architecture, the language of thought—at the top, knowledge layer—is a classical, first-order, non-indexical language; the indexical “now” features at a lower, perceptuo-motor layer. It is the reasoning process that cuts across both layers, giving rise to indexical thinking. Thus, we trade indexical thoughts for indexical thought. The proposed treatment is shown to supersede previous approaches with respect to the proposed criteria.