“Here we must make one of those inductive applications of the law of continuity which have produced such great results in all of the positive sciences. We must extend the law of insistency into the future. Plainly, the insistency of a future idea with reference to the present is a quantity affected by the minus sign; for it is the present that affects the future, if there be any effect, not the future that affects the present.”

Source: Opus Tertium, c. 1267, Ch. 14 as quoted in J. H. Bridges, The 'Opus Majus' of Roger Bacon (1900) Vol.1 http://books.google.com/books?id=6F0XAQAAMAAJ Preface pp.x-xi
Context: All these foregoing sciences are, properly speaking, speculative. There is indeed in every science a practical side, as Avicenna teaches in the first book of his Art of Medicine. Nevertheless, of Moral Philosophy alone can it be said that it is in the special and autonomatic sense practical, dealing as it does with human conduct with reference to virtue and vice, beatitude and misery. All other sciences are called speculative: they are not concerned with the deeds of the present or future life affecting man's salvation or damnation. All procedures of art and of nature are directed to these moral actions, and exist on account of them. They are of no account except in that they help forward right action. Thus practical and operative sciences, as experimental alchemy and the rest, are regarded as speculative in reference to the operations with which moral or political science is concerned. This science is the mistress of every department of philosophy. It employs and controls them for the advantage of states and kingdoms. It directs the choice of men who are to study in sciences and arts for the common good. It orders all members of the state or kingdom so that none shall remain without his proper work.

Gouverneur Morris to Robert Walsh ( February 5, 1811 http://www.bgdlegal.com/clientuploads/Publications/Publications/John%20Bush%20-%20Gouverneur%20Morris.pdf)
1810s

The Law of Mind (1892)

1960, The New Frontier
Context: For the harsh facts of the matter are that we stand on this frontier at a turning-point in history. We must prove all over again whether this nation — or any nation so conceived — can long endure — whether our society — with its freedom of choice, its breadth of opportunity, its range of alternatives — can compete with the single-minded advance of the Communist system. Can a nation organized and governed such as ours endure? That is the real question. Have we the nerve and the will? Can we carry through in an age where we will witness not only new breakthroughs in weapons of destruction — but also a race for mastery of the sky and the rain, the ocean and the tides, the far side of space and the inside of men's minds? Are we up to the task — are we equal to the challenge? Are we willing to match the Russian sacrifice of the present for the future — or must we sacrifice our future in order to enjoy the present? That is the question of the New Frontier. That is the choice our nation must make — a choice that lies not merely between two men or two parties, but between the public interest and private comfort — between national greatness and national decline — between the fresh air of progress and the stale, dank atmosphere of "normalcy" — between determined dedication and creeping mediocrity. All mankind waits upon our decision. A whole world looks to see what we will do. We cannot fail their trust, we cannot fail to try.

Variant: Change is the law of life. And those who look only to the past or present are certain to miss the future.

The Law of Mind (1892)

Source: The National System of Political Economy (1841), Ch. 12

Source: Money

Source: Postmodernism: Or, The Cultural Logic of Late Capitalism (1991), Chapter 1: The Cultural Logic of Late Capitalism