31 Dec 2008

Bergson, Time and Free Will, Chapter 1, §40 "This is Just the Case with Differences of Intensity in Sensations of Light"

by Corry Shores
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Bergson, Time and Free Will

(Essai sur les données immédiates de la conscience)

Chapter I, "The Intensity of Psychic States"

Part XIII: "Sensation of Light"

§40 "This is Just the Case with Differences of Intensity in Sensations of Light. Delboeuf's Underlying Postulate"

Although Delboeuf's ring experiment might lead us to believe that we can quantify the intensity of all sensations, his experiment really only showed that this works for his specific case of luminosity. For, color also lies on a spectrum of intensity, so we are able to say that orange, for example, is just as distant to green as it is to red.

But in our experiences, we frequently perceive continuous changes of luminosity, but almost never continuous changes of color through the spectrum.

For Bergson, the changes in shades between white and black are qualitative. Hence the changes are discontinuous. So Bergson does in fact think that we may measure the changes of intensity between luminosities by counting them. But that does not make any one of those changes greater or less than another; they are merely different.

And even if we counted the successive shades between luminosities A and B, and found that figure to equal the sum between B and C, we still cannot trust this as proof that intensity is quantitative. For,

1) it would be an imprecise estimate,

2) the figure would vary considerably between people, and

3) when the luminosities become higher, viewers will have to work harder to make their estimates, which will interfere with the accuracy.

In fact, if we look at Delboeuf's results we find such inconsistencies.

Also, when we change the luminosity, we create a succession of elementary contrasts. So for Delboeuf's findings to hold, we need first be sure that the succession of elementary contrasts are of equal quantities. In addition, Delboeuf must prove one more thing,

a) that each change in luminosity has the same magnitude of difference, and

b) that any given shade is the sum of the differences all the differences leading up to it from zero.

The above presumptions constitute Fechner's psychophysical postulate, which Bergson will now examine.

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Images from the pages summarized above, in the English Translation [click on the image for an enlargement]:

Images from the pages summarized above, in the original French [click on the image for an enlargement]:

Bergson, Henri. Time and Free Will: An Essay on the Immediate Data of Consciousness, Transl. F. L. Pogson, (New York: Dover Publications, Inc., 2001).

Available online at:


French text from:

Bergson, Henri. Essai sur les données immédiates de la conscience. Originally published Paris: Les Presses universitaires de France, 1888.


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