ABSTRACT
When humans use words like “apple” or “eagle,” we recognize the referential relation that holds between such signs and the things for which they stand. Referential relations can, for instance, be distinguished from causal relations: The word “eagle” does not cause a particular bird to appear or result in a particular pattern of behavior. Instead, the word “stands for,” or “conjures up images of,” an object even when that object cannot be seen.
