Sam Alma at Aeon Magazine: You are standing on a boat that is drifting down a placid river. You watch the trees on the shore glide along. For a moment, it looks like the trees themselves are moving – not your boat. But this, of course, is mere appearance: the trees are still, and it is your boat that moves. This parallax effect was described by medieval philosophers, but it may be more familiar in another form: when you’re sitting on a train slowly rolling out of the station, it can seem like it is the stationary train next to yours that is departing instead.
A handful of 14th-century scholastic thinkers wondered how this parallax effect came about. What explains our perceptual error? Let’s call this the problem of erring. In finding a solution, the medieval philosophers had to take into account another observation: nonhuman animals err too. According to scholastic orthodoxy, human and nonhuman animals were alike in being animals. Even so, within this category, humans occupied a special place: they are the only type of animal that is endowed with an intellect, a rational soul. They are, in medieval parlance, rational animals.
What happens in the case of erring? Do nonhuman animals err? Together, these two questions posed a considerable philosophical challenge to William of Ockham (c1287-1347), Adam Wodeham (c1295-1358) and Gregory of Rimini (c1300-1358). The first question, as we will see, was answered that erring is an act of the intellect. To the second, the answer was a tentative yes, as empirical observations suggest. Together, these answers put the medieval philosophers in an awkward position: nonhuman animals carry out acts of the intellect, yet without having one. Call this the problem of nonhuman erring.
While centuries old, this debate reveals a question that is relevant for today’s debates on nonhuman minds. How much are we willing to give up in order to hold on to our basic assumptions? Nonhuman minds continue to be a source of discord. After all, we simply cannot infer with absolute certainty from the outside what is going on in the inside of someone else, let alone a nonhuman being.
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