“Judged by the only standards which are admissible in a pure doctrine of numbers i is imaginary in the same sense as the negative, the fraction, and the irrational, but in no other sense; all are alike mere symbols devised for the sake of representing the results of operations even when these results are not numbers (positive integers).”
Source: The Number-System of Algebra, (1890), p. 86; Reported in Moritz (1914, 282)
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Henry Burchard Fine 3
American academic 1858–1928Related quotes
Source: Mathematics and the Physical World (1959), pp. 49-50.
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Source: Mathematics and the Physical World (1959), p. 51.
Source: Mathematical Thought from Ancient to Modern Times (1972), pp. 252-253.

Vol. I: Arithmetical Algebra Preface, p. iv
A Treatise on Algebra (1842)

Diophantos of Alexandria: A Study in the History of Greek Algebra (1885)

That these are the laws employed in the demonstration of the principal theorems in Algebra, a slight examination of the processes will easily shew ; but they are not confined to symbols of numbers ; they apply also to the symbol used to denote differentiation.
p. 237 http://books.google.com/books?id=8lQ7AQAAIAAJ&pg=PA237; Highlighted section cited in: George Boole " Mr Boole on a General Method in Analysis http://books.google.com/books?pg=PA225-IA15&id=aGwOAAAAIAAJ&hl," Philosophical Transactions, Vol. 134 (1844), p. 225; Other section (partly) cited in: James Gasser (2000) A Boole Anthology: Recent and Classical Studies in the Logic of George Boole,, p. 52
Examples of the processes of the differential and integral calculus, (1841)

Footnote: The apparent advantage of the generality of this definition of number disappears as soon as we consider complex numbers. According to my view, on the other hand, the notion of the ratio between two numbers of the same kind can be clearly developed only after the introduction of irrational numbers.
Stetigkeit und irrationale Zahlen (1872)