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This thesis is about the nature, and more specifically the ontological status of the objects of perception (that is, perceptible qualities) in Aristotle. It defends a realist interpretation. It contends that perceptible qualities are irreducible items in Aristotle’s ontology, and that he holds that they can entertain a perception-independent existence.

The thesis offers a way to understand the observation that in the extant works Aristotle often speaks of qualities such as colours, sounds, odours, flavours and tangible qualities (like hotness, dryness, wetness) as features of material objects in our surroundings. It defends the idea that Aristotle speaks of them in this way because he is committed to the view that perceptible qualities are real features of the objects. It specifies the scope of his realism about them by examining their status from various angles. It argues that Aristotle develops a non-reductive approach towards perceptible qualities, on the basis that reductive, if not eliminative, approaches fail to preserve the differences observed by common people between these qualities and some other features that are considered to be ontologically basic. It also establishes Aristotle’s realism from another angle: for him, perceptible qualities can continue to exist in material objects even when they are not being perceived. In this sense, qualities are “affections” of material objects, being features the objects have come to possess after undergoing changes and being affected. Besides all this, the thesis tackles the question of perception-independent existence in the context of causal processes, where perceptible qualities are understood as dispositional properties residing in material objects. The thesis defends the view that perceptible qualities can actualise their potentialities not only when they affect sentient beings and make themselves perceived, but also in the absence of being perceived, namely, when they produce non-perceptual changes in bodies, sentient or insentient.