Things can have various kinds of properties: properties such as shapes, colours, and sounds are low-order properties; properties that depend on their instantiation on the former are higher-order properties. Suppose, as is standard in the philosophical literature, that low-order properties are perceivable. Are some higher-order properties perceivable too? The list of candidates is long, including natural and artificial kinds, organizational properties of different kinds, affordances, expressive and emotional properties, agential, intentional and even semantic properties, aesthetic and moral properties, and causal relations. Despite a lively debate on this topic in recent philosophy, the question is far from settled. The Higher-Order Perceivable Properties project (HOPP) will advance this debate by pursuing a novel and groundbreaking approach. HOPP’s aim is to identify philosophically sound necessary and jointly sufficient conditions for a property to be perceivable which may apply both to low-order and to higher-order properties. This will enable HOPP to systematically assess the perceivability of each candidate higher-order property according to a unitary criterion.
HOPP’s results will have wider philosophical implications. First, a unitary criterion for property perceivability can explain if and how the perception of higher-order properties is hierarchically organized, just as the perception of such properties is with respect to the perception of the low-order properties on which they depend. Second, it may give a principled answer to the question of up to what extent the perception of higher-order properties is cognitively penetrated, i.e., it is influenced by the contents of cognitive states of the mind. Third, by assessing up to what extent higher-order properties are objects of noticing, it may help one to clarify the relationship between perception and attention. Moreover, it may provide the theoretical foundations for future empirical research, as the unitary criterion may be tested for its empirical adequacy by checking whether the apprehension of the perceivable higher-order properties is indeed implemented in the perceptual areas of the brain. Finally, identifying which higher-order properties are perceivable may contribute to the development of effective artificial intelligence in the robotics field, especially in contexts where human-robot interaction is important, and to the design of artefacts that are more easily recognizable and usable.