“In its present state of development psychology must be thought of as a young science. There is only one field in which it is relatively well established and in which it has advanced steadily: this is the psychology of sensation and perception. The scientific character of this field is fully recognized. Its findings are based almost entirely on experimental evidence, and even when its theories are in conflict one feels that as far as method is concerned it stands on relatively firm ground. The situation is different with the psychology of will, of needs, and of personality despite the fact that these fields have always attracted popular interest. As recently as fifteen years ago it was assumed that they, by their very nature, were not amenable to scientific methods. The little experimental work that had been done seemed too artificial and abstract to give an insight into the real processes. It was generally accepted that experimental investigations of these elusive and highly complicated processes were intrinsically impossible, at least in so far as human beings are concerned. Thus in Europe these problems were treated in a half-literary, half-philosophical way, and in America the tendency was to study individual differences by means of tests.”

Source: 1930s, Principles of topological psychology, 1936, p. viii.

Source: Management and technology, Problems of Progress Industry, 1958, p. 21-22

Source: Constructing the subject: Historical origins of psychological research. 1994, p. 1; Introduction

Introductory
The Grammar of Science (1900)

George Boole, " Solution of a Question in the Theory of Probabilities http://books.google.nl/books?id=9xtDAQAAIAAJ&pg=PA32" (30 November 1853) published in The London, Edinburgh and Dublin Philosophical Magazine and Journal of Science‬‎ (January 1854), p. 32
1850s

Source: How Maps Work: Representation, Visualization, and Design (1995), p. 1

Introductory
The Grammar of Science (1900)

From Kant to Hilbert (1996)
Context: Mathematics is in its development entirely free and is only bound in the self-evident respect that its concepts must both be consistent with each other, and also stand in exact relationships, ordered by definitions, to those concepts which have previously been introduced and are already at hand and established. In particular, in the introduction of new numbers, it is only obligated to give definitions of them which will bestow such a determinacy and, in certain circumstances, such a relationship to the other numbers that they can in any given instance be precisely distinguished. As soon as a number satisfies all these conditions, it can and must be regarded in mathematics as existent and real.

Source: The Ape that Kicked the Hornet's Nest (2013), p. 251