“The Essential Differentiae of Things Are Unknown to Us". Thomas Aquinas on the Limits of Knowability of Natural Substances

Thomas Aquinas is often presented as a philosopher with a realist and optimistic attitude toward human knowledge. This is essentially true. Nevertheless, there are texts where Aquinas underscores the limits of our knowledge of natural things. For example, he states that we arrive at knowing and naming the substance of a thing only through knowing its accidents. Aquinas makes three main claims about this process: first, the essential principles of natural things are unknown to us; second, the accidents of a thing give a great contribution to the knowledge of what a thing is; third, we impose names to things moving from their accidents. Such claims may be read as introducing a sceptical concern. On the contrary, they express a form of phenomenical realism, which Aquinas reconciles with representationalism in knowledge.