Abstract
SACCHERI, in his “Logica Demonstrativa,” published in 1697, ten years after Newton's “Principia Mathematica,” lays down a distinction between real and nominal definitions which should be kept in mind if we are to do justice to Newton. Euclid defines a square as a four-sided figure the sides of which are all equal, and the angles of which are all right-angles. That is what he means by the name “square.” It is a nominal definition. It remains to be shown that such a figure exists. This is done in Book I., Prop. 46. The definition then becomes real. Euclid is not guilty of the error of presupposing the existence of the figure.
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CUNNINGHAM, E. Relativity: The Growth of an Idea. Nature 106, 784–786 (1921). https://doi.org/10.1038/106784a0
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DOI: https://doi.org/10.1038/106784a0