Do You See Red as I See Red? On Inter-Individual Variability and Phenomenal Distance

Most of us assume that we do. A tomato looks red, the sky looks blue, and everybody agrees—so what is there to question, right?

Sascha Benjamin Fink, Director of Research of the Centre of Philosophy and AI Research at FAU Erlangen and Affiliated Professor at the Centre for the Study of Perceptual Experiences at the University of Glasgow, explores the century-old puzzle of what if two people, under the same conditions, have completely different inner experiences but never realize it?

This idea, known as the “inverted spectrum” (IS), was first introduced by John Locke in the 17th century. Imagine two people who both call a tomato “red,” but internally, one sees what the other would call “green.” They’d never know, because they’ve learned to use the labels not vis-à-vis their own experiences, but concerning external sources – tomatoes and the sky. The question Locke raised is still deeply relevant today: How do we know if someone else experiences the world like we do?

Fink’s talk, Distance in Phenomenal Spaces, will tackle this question using tools from philosophy and psychology. Fink draws on structuralism, which argues that experiences are defined by their relationships to other experiences. In other words, red is red not because of what it feels like in isolation, but because of how it compares to orange, blue, or green.

But can we really map out those relationships between experiences — what Fink refers to as a “phenomenal space”? This is where things become challenging. People’s judgments about how different two colors feel can be surprisingly inconsistent. This raises questions about whether such spaces can ever be measured in a reliable way.

At this year’s Consciousness Research Network (CoRN 2025) conference, we are excited to welcome Sascha Fink as a keynote speaker. Don’t miss his thought-provoking session on how something as simple as the color red might reveal the deeper structure of conscious experience.

Written by: Payachana Victoria Chareunsouk