“The things which philosophy attempts to teach by reasoning, poverty forces us to practice.”

The Virtue of Selfishness (1964)

Stobaeus, iv. 32a. 19
Quoted by Stobaeus

Money.
Notes from Life (1853)

Persecution and the Art of Writing (1952), Introduction

Meistens belehrt uns erst der Verlust über den Wert der Dinge.
Source: Parerga and Paralipomena (1851), Aphorisms on the Wisdom of Life

Source: Science and Hypothesis (1901), Ch. VI: The Classical Mechanics (1905) Tr. https://books.google.com/books?id=5nQSAAAAYAAJ George Bruce Halstead
Context: What is mass? According to Newton, it is the product of the volume by the density. According to Thomson and Tait, it would be better to say that density is the quotient of the mass by the volume. What is force? It, is replies Lagrange, that which moves or tends to move a body. It is, Kirchhoff will say, the product of the mass by the acceleration. But then, why not say the mass is the quotient of the force by the acceleration?
These difficulties are inextricable.
When we say force is the cause of motion, we talk metaphysics, and this definition, if one were content with it, would be absolutely sterile. For a definition to be of any use, it must teach us to measure force; moreover that suffices; it is not at all necessary that it teach us what force is in itself, nor whether it is the cause or the effect of motion.
We must therefore first define the equality of two forces. When shall we say two forces are equal? It is, we are told, when, applied to the same mass, they impress upon it the same acceleration, or when, opposed directly one to the other, they produce equilibrium. This definition is only a sham. A force applied to a body can not be uncoupled to hook it up to another body, as one uncouples a locomotive to attach it to another train. It is therefore impossible to know what acceleration such a force, applied to such a body, would impress upon such an other body, if it were applied to it. It is impossible to know how two forces which are not directly opposed would act, if they were directly opposed.
We are... obliged in the definition of the equality of the two forces to bring in the principle of the equality of action and reaction; on this account, this principle must no longer be regarded as an experimental law, but as a definition.<!--pp.73-74

Andere wieder, von diesen Wahrheitsforschern, schmelzen Philosophie und Religion zu einem Kentauren zusammen, den sie Religionsphilosophie nennen; Pflegen auch zu lehren, Religion und Philosophie seien eigentlich das Selbe;—welcher Sah jedoch nur in dem Sinne wahr zu seyn scheint, in welchem Franz I., in Beziehung auf Karl V., sehr versöhnlich gesagt haben soll: „was mein Bruder Karl will, das will ich auch,”—nämlich Mailand, Wieder andere machen nicht so viele Umstände, sondern reden geradezu von einer Christlichen Philosophie;—welches ungefähr so herauskommt, wie wenn man von einer Christlichen Arithmetik reden wollte, die fünf gerade seyn ließe. Dergleichen von Glaubenslehren entnommene Epitheta sind zudem der Philosophie offenbar unanständig, da sie sich für den Versuch der Vernunft giebt, aus eigenen Mitteln und unabhängig von aller Auktorität das Problem des Daseyns zu lösen.
Sämtliche Werke, Bd. 5, p. 155, E. Payne, trans. (1974) Vol. 1, pp. 142-143
Parerga and Paralipomena (1851), On Philosophy in the Universities

The Virtue of Selfishness (1964)