Quality is, in the first place, the character identical with being: so identical, that a thing ceases to be what it is, if it loses its quality. Quantity, on the contrary, is the character external to being, and does not affect the being at all.
 Georg Wilhelm Friedrich Hegel, Science of Logic (1816). copy citation

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Author Georg Wilhelm Friedrich Hegel
Source Science of Logic
Topic quality contrary
Date 1816
Language English
Reference
Note Translated by William Wallace
Weblink http://www.gutenberg.org/files/55108/55108-h/55108-h.htm

Context

“Each of the three spheres of the logical idea proves to be a systematic whole of thought-terms, and a phase of the Absolute. This is the case with Being, containing the three grades of quality, quantity, and measure. Quality is, in the first place, the character identical with being: so identical, that a thing ceases to be what it is, if it loses its quality. Quantity, on the contrary, is the character external to being, and does not affect the being at all. Thus e.g. a house remains what it is, whether it be greater or smaller; and red remains red, whether it be brighter or darker. Measure, the third grade of being, which is the unity of the first two, is a qualitative quantity.” source