Howard Margolis (1998) A "delusion" Defended. Psycoloquy: 9(45) Cognitive Illusion (10)

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PSYCOLOQUY (ISSN 1055-0143) is sponsored by the American Psychological Association (APA).
Psycoloquy 9(45): A "delusion" Defended

Reply to Topper and Manufo & Tijsseling on Cognitive-Illusion

Howard Margolis
Harris School
University of Chicago
Chicago IL 60637


Topper (1998) and Munafo & Tijsseling (1998) each see a problem with the solid spheres Tychonic model shown in Margolis (1998). Neither of the problems actually exists.


blindsight, cognitive illusion, mental image, persuasion, psychology of science.
1. Topper (1998) writes that Mars does not move around the sun in the solid spheres version of the system described in Margolis (1998). But of course Mars does move around the sun. What else would an object in heliocentric orbit do? As Tycho and observations require, each of the planetary orbits rotates in place relative to the sun, as the entire Tychonic solar system is carried around on its annual revolution. Topper suggests that that is impossible, and that I am deluded not to share that insight. I would be grateful for further reports on this from other readers. Presumably Topper has taken the moment required to make the cutout from Figs. 5a & 5b of my article, and see it move. Are there other readers who have done that but nevertheless still see a collision?

Margolis (1998) Figure 5:

2. Munafo & Tijsseling (1998), on the other hand, agree with me that Tycho's illusion is indeed an illusion. But since these heavenly spheres must completely fill the space between the fixed stars and the Earth/moon region, they argue that there would be another sort of solid spheres problem. But the single Tychonic sphere represented by Fig. 5a of my target article does solidly fill the entire required space. The rotating orbits of the five Tychonic planets are then carried within that single Tychonic sphere, exactly analogous to the way the rotating epicycles of the Ptolemaic planets are carried within their individual Ptolemaic spheres. There is indeed no room for, but also no point to, the solid "sphere of Mars" that Manufo & Tijsseling describe. Since there would be no such sphere, it could not cause the problem they envision.

3. According to Topper, "Tycho's system, as he conceived it, did not entail spheres." But that is not what Tycho said: he said that for some time after he discovered the system he was held back from believing it because of the solid spheres problem. Topper has this just backwards. See the very detailed account in Gingerich & Westman (1989).


Gingerich, O. & Westman R. (1989). The Wittich Connection. American Philosophical Society.

Harris, L. (1998), The Mars/sun Collision Illusion: motion is not visualizable in two different reference frames simultaneously PSYCOLOQUY 9(34)

Margolis, H. (1998) Tycho's Illusion: How It Lasted 400 Years, and What That Implies About Human Cognition. PSYCOLOQUY 9(32)

Munafo, M. & Tijsseling, A. (1998) Movement in a Solid Sphere:. PSYCOLOQUY 9(44) Cognitive Illusion (9)

Topper, D. (1998) Margolis's Delusion: a Critique of "tycho's Illusion". PSYCOLOQUY 9(42)

Volume: 9 (next, prev) Issue: 45 (next, prev) Article: 10 (next prev first) Alternate versions: ASCII Summary