“A finished or even a competent reasoner is not the work of nature alone… education develops faculties which would otherwise never have manifested their existence. It is, therefore, as necessary to learn to reason before we can expect to be able to reason, as it is to learn to swim or fence, in order to attain either of those arts. Now, something must be reasoned upon, it matters not much what it is, provided that it can be reasoned upon with certainty. The properties of mind or matter, or the study of languages, mathematics, or natural history may be chosen for this purpose. Now, of all these, it is desirable to choose the one… in which we can find out by other means, such as measurement and ocular demonstration of all sorts, whether the results are true or not.
.. Now the mathematics are peculiarly well adapted for this purpose, on the following grounds:—
1. Every term is distinctly explained, and has but one meaning, and it is rarely that two words are employed to mean the same thing.
2. The first principles are self-evident, and, though derived from observation, do not require more of it than has been made by children in general.
3. The demonstration is strictly logical, taking nothing for granted except the self-evident first principles, resting nothing upon probability, and entirely independent of authority and opinion.
4. When the conclusion is attained by reasoning, its truth or falsehood can be ascertained, in geometry by actual measurement, in algebra by common arithmetical calculation. This gives confidence, and is absolutely necessary, if… reason is not to be the instructor, but the pupil.
5. There are no words whose meanings are so much alike that the ideas which they stand for may be confounded.
…These are the principal grounds on which… the utility of mathematical studies may be shewn to rest, as a discipline for the reasoning powers. But the habits of mind which these studies have a tendency to form are valuable in the highest degree. The most important of all is the power of concentrating the ideas which a successful study of them increases where it did exist, and creates where it did not. A difficult position or a new method of passing from one proposition to another, arrests all the attention, and forces the united faculties to use their utmost exertions. The habit of mind thus formed soon extends itself to other pursuits, and is beneficially felt in all the business of life.”

Part 1.3 Rights of Man
1790s, Rights of Man, Part I (1791)

Academy of Achievement interview (1991)
Context: Reason alone will not serve. Intuition alone can be improved by reason, but reason alone without intuition can easily lead the wrong way. They both are necessary. The way I like to put it is that when I have an intuition about something, I send it over to the reason department. Then after I've checked it out in the reason department, I send it back to the intuition department to make sure that it's still all right. That's how my mind works, and that's how I work. That's why I think that there is both an art and a science to what we do. The art of science is as important as so-called technical science. You need both. It's this combination that must be recognized and acknowledged and valued.

Source: Island

During the Second Anglo-Dutch War.
The myth of the free market: the role of the state in a capitalist economy by Mark Anthony Martinez, p. 116 http://books.google.co.uk/books?id=M97-cI2V080C&pg=PA116&dq=%22What+matters+this+or+that+reason%3F+What+we+want+is+more+of+the+trade+which+the+Dutch+now+have.%22&hl=en&ei=pePHTKXJDoqOjAfo_vFK&sa=X&oi=book_result&ct=result&resnum=5&ved=0CD0Q6AEwBA#v=onepage&q=%22What%20matters%20this%20or%20that%20reason%3F%20What%20we%20want%20is%20more%20of%20the%20trade%20which%20the%20Dutch%20now%20have.%22&f=false

Materiae ne quaere modum; sed perspice vires
Quas ratio, non pondus habet; ratio omnia vincit.
Book IV, line 924, as reported in Harbottle's Dictionary of Quotations (classical) (1897), p. 130.
Astronomica

X. Concerning Virtue and Vice.
On the Gods and the Cosmos
Context: The doctrine of virtue and vice depends on that of the soul. When the irrational soul enters into the body and immediately produces fight and desire, the rational soul, put in authority over all these, makes the soul tripartite, composed of reason, fight, and desire. Virtue in the region of reason is wisdom, in the region of fight is courage, in the region of desire is temperance; the virtue of the whole soul is righteousness. It is for reason to judge what is right, for fight in obedience to reason to despise things that appear terrible, for desire to pursue not the apparently desirable, but, that which is with reason desirable. When these things are so, we have a righteous life; for righteousness in matters of property is but a small part of virtue. And thus we shall find all four virtues in properly trained men, but among the untrained one may be brave and unjust, another temperate and stupid, another prudent and unprincipled. Indeed, these qualities should not be called virtues when they are devoid of reason and imperfect and found in irrational beings. Vice should be regarded as consisting of the opposite elements. In reason it is folly, in fight, cowardice, in desire, intemperance, in the whole soul, unrighteousness.
The virtues are produced by the right social organization and by good rearing and education, the vices by the opposite.

Source: House of Leaves

Source: Thomas Reid's Inquiry and Essays

Jane Sinnett, trans 1846 p.110
The Vocation of Man (1800), Faith