The philosopher David Hume believed that, to understand abstract concepts, humans needed to summon a mental image to picture the idea. But since Hume’s time in the 18th century, we now have a more nuanced understanding of the human brain’s complexity—and our philosophy might be due for some upgrades, according to a new study.
Scientists estimate that roughly 4% to 5% of the population experience aphantasia, or the inability to form mental images. People can be either born with aphantasia or develop it later, but it’s typically not considered a disability or medical condition. But aphantasia isn’t known to prevent people from having a firm grasp of abstract ideas—things like “triangle,” “friend,” or “memory,” explained Uku Tooming and Roomet Jakapi, philosophers at the University of Tartu in Estonia, in a statement. So, what’s going on here?
In a recent paper published in Neuropsychologia, Tooming and Jakapi present a challenge to Hume; that is, abstract thought might not be as grounded in images as we might believe.
Imagine an apple…
As a concept, aphantasia first entered the scientific discourse in 1880, when British geneticist (and eugenics pioneer) Francis Galton described interacting with individuals who “protested that mental imagery was unknown to them.” But the phenomenon was officially termed much later, in 2015. In other words, although people knew about aphantasia for a long time, it has only been in the past decade or so that scientists have started to systematically investigate the condition, according to the paper.
This includes philosophers, who typically struggle to ignore unexpected twists in human cognition. The link between visualization and reasoning has always been foundational to the history of philosophy, the researchers explained in the paper. For example, Hume and empirical thinkers like 18th-century Irish philosopher George Berkeley believed that thought and knowledge emerged from sensory experiences, with the former saying that ideas are “faint images” of “thinking and reasoning.”
…Unless you can’t?
However, Tooming and Jakapi argued in the paper that aphantasia “poses a problem” for Hume’s view of abstractions. In typical philosophy fashion, the pair demonstrated the validity of their claim by examining four possible scenarios of “how Hume would respond” to their challenge. For instance, Hume (or his supporters) may argue that aphantasics could rely on other sensory factors or linguistic cues to “visualize” ideas.
However, as Tooming and Jakapi counter in the paper, experimental evidence suggests that some aphantasics lack imagery across other types of sensory experiences, and yet are still capable of abstraction. Then there’s the easy way out: Okay, maybe aphantasics are an exception to the rule. But the authors took issue with that response, as the challenge is “not merely one of accommodating an exception but of explaining how abstraction is even possible without reliance on the imagistic processes that Hume sees as essential.”
Picking apart the brain
From what we understand of aphantasia so far, there isn’t evidence to suggest that aphantasics have a wildly different psychology from non-aphantasics—therefore, perhaps it’s actually the case that human abstraction isn’t as dependent on mental imagery as it may seem, they added. In that sense, the challenge doesn’t just address Hume’s ideas but other theories that “try to ground various higher-level mental phenomena in the capacity to generate mental imagery,” Tooming and Jakapi wrote.
In any case, the study demonstrates the complex and flexible nature of the human mind—something that, in the centuries since Hume’s time, we still don’t fully understand. Although Hume’s theories should be understood as a product of their time, considering the limitations could serve as a “productive constraint on future accounts of abstraction and higher cognition,” the authors concluded.
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