Aphantasia, the inability to form mental images, poses a serious challenge to an influential theory of abstract thought in the history of philosophy. The study by researchers at the University of Tartu suggests that mental imagery may play a less central role in human thought than has long been assumed and that the mind is more flexible in how it represents the world than many theories allow.
Most of us, when asked to think about triangles, dogs, or justice, spontaneously conjure up some kind of mental picture: a red triangle drawn on a blackboard, a scruffy terrier, a courtroom scene. The 18th-century Scottish philosopher David Hume believed this was not just a habit but a necessity. In his view, the mind cannot deal with pure abstractions directly and always needs a concrete mental image to work with first. To think about triangles in general, you must first picture a specific one. To think about justice, you must mentally replay some vivid scene of fairness or its violation.
But what about people who cannot form mental images at all? People with severe aphantasia draw a complete blank when asked to visualize a rainbow, picture a close friend's face, or imagine their childhood bedroom. There is simply nothing there. Yet they can reason about rainbows, recognize their friends, and reflect on their past. And they can engage with abstract concepts like geometry, morality, and mathematics just as well as anyone else.
In a paper published in Neuropsychologia , University of Tartu Associate Professor of Theoretical Philosophy Uku Tooming and Associate Professor of History of Philosophy Roomet Jakapi argue that aphantasia presents a direct challenge to Hume's theory, and to imagistic models of cognition more broadly. As Tooming puts it: "If abstract thought genuinely required mental imagery, people with aphantasia should struggle to think abstractly. They do not."
How can abstract thought work without images?
The authors consider and reject several defences of the Humean account. One possibility is that aphantasics perform abstraction using imagery from non-visual modalities, for instance, by relying on auditory or tactile imagery rather than visual images. However, this is dismissed considering in light of the existence of multimodal aphantasics, who lack imagery across all sensory modalities.
Another defence appeals to involuntary imagery, suggesting that even if aphantasics cannot deliberately form images, they might still rely on imagery that arises spontaneously. This, too, is rejected on the grounds that the kind of imagery required for Humean abstraction is at least partially voluntary and that severe aphantasics lack such imagery. A further proposal invokes spatial imagery, such as a schematic sense of shape or arrangement without visual detail, for example, grasping the geometric relations of a triangle without picturing one. Yet this defence also fails because such spatial representations lack the sensory richness that Hume's account takes to be essential.
Finally, the suggestion that aphantasics could perform abstraction by means of language, for instance, by reasoning with the word "triangle" rather than an image, is rejected because the Humean framework requires imagery for understanding abstract concepts that are expressed in language.
The most compelling defence appeals to intact unconscious imagery in aphantasics. On this view, even if individuals cannot consciously visualize a rainbow or a triangle, they may still employ mental imagery unconsciously when engaging in abstract thought. The paper ultimately rejects this line of response as well, citing limited evidence for unconscious imagery in aphantasia and recent studies indicating an absence of imagery overall, both conscious and unconscious.
More than a philosophical exception
Finally, the paper addresses a metatheoretical response that treats aphantasia as a harmless exception. This approach suggests that Hume's theory could still hold for most people, even if it does not apply to aphantasics. However, the authors argue that this fails because if aphantasics do not require imagery for abstract thinking, it has broader repercussions for understanding their cognitive processes generally. It would imply a radical difference between the psychology of aphantasics and non-aphantasics, which is highly implausible. Aphantasia, therefore, cannot be treated as a mere exception, but instead poses a substantive challenge to imagistic accounts of thought.
The findings have implications beyond the history of philosophy. Imagistic theories of cognition remain influential in contemporary cognitive science and philosophy of mind.
