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The kind of knowledge which is supported only by observations and is not yet proved must be carefully distinguished from the truth; it is gained by induction, as we usually say. Yet we have seen cases in which mere induction led to error.

— Leonhard Euler

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Source: Opera Omnia, ser. 1, vol. 2, p. 459 Spcimen de usu observationum in mathesi pura, as quoted by George Pólya, Induction and Analogy in Mathematics Vol. 1, Mathematics and Plausible Reasoning (1954)
Source quality: Secondhand citation Quoted from another book or article rather than from the original.

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Quote text and notes from Wikiquote: Leonhard Euler (page history), available under CC BY-SA 4.0. Source quality and labels are our own summary of what Wikiquote records.