 One challenge to this view of cognition is its implication for abstract concepts. It’s one thing to say that the concept HAMMER involves the activation of circuits related to hand shape; it’s quite another to identify representations tied to a particular sensory modality underlying such concepts as TRUTH, DEMOCRACY, ENTROPY, and NINETEEN (Adams &amp; Campbell 1999, Brewer 1999). Logical concepts are also a challenge. Prinz suggests as a perceptual basis for the concept of disjunction that it is based on feelings of hesitation. However, his more considered view seems to be that logical concepts are best understood as operations, not representations. The resulting theory is one in which thoughts lack logical form. The trouble is that this makes it difficult to see how to distinguish logically equivalent thoughts. A related problem is that, since composition for Prinz does not yield structurally complex representations, there seems to be nothing to distinguish the type of contents associated with judgements (propositional contents) from those associated lists or even single concepts (for related discussion Fodor 2003). Finally, there are difficulties regarding how to interpret behavioral and neurological evidence that is supposed to support Prinz and Barsalou’s case against amodal representations. For example, Machery (2007) points out that proponents of amodal representations typically suppose that imagery is useful in solving certain types of problems. So to argue against amodal representations, it is not enough to show that sensory representations show up in a task in which experimental subjects are not explicitly told to visualize a solution, since the use of sensory-based imagery in a task is perfectly compatible with there also being amodal representations in play. (For further critical discussion of the form of empiricism that is opposed to amodal representations, see Weiskopf 2007, Dove 2009, and Mahon 2015).