Summary: A Treatise of Human Nature

Introduction

Hume's scepticism emerges from the very first lines of the Introduction: deploring that ignorance, which we still lie under in the most important questions, that can come before the tribunal of human reason, he observes how easy it is to perceive the weak foundation even of those systems, which have obtain'd the greatest credit, and have carry'd their pretensions highest to accurate and profound reasoning. This holds true even in the systems of the most eminent philosophers. In the end, such a state of affairs seems to have drawn disgrace upon philosophy itself ¹.

The clearest symptom of this crisis, of this failure, is the absence of any consensus. There is no agreement on anything: There is nothing which is not the subject of debate, and in which men of learning are not of contrary opinions. The most trivial question escapes not our controversy, and in the most momentous we are not able to give any certain decision. ².

It is metaphysics that is most affected by these endless debates:

From hence in my opinion arises that common prejudice against metaphysical reasonings of all kinds [...] We have so often lost our labour in such researches, that we commonly reject them without hesitation ³.

Thus, in the end, we are led to a generalised scepticism regarding all these interminable questions: And indeed nothing but the most determin'd scepticism, along with a great degree of indolence, can justify this aversion to metaphysics ⁴.

This image of metaphysics as an endless battlefield would later inspire Kant. It appears in the Critique of Pure Reason, from the very first page of the preface to the first edition: The battlefield of these endless controversies is called metaphysics ⁵.

Far from resigning himself to this admission of impotence, Hume seeks a way to resolve these problems and put an end to these disagreements. To achieve this, we must refocus our attention on human nature: this must be the starting point of all our investigations.

Indeed, ’Tis evident, that all the sciences have a relation, greater or less, to human nature; and that however wide any of them may seem to run from it, they still return back by one passage or another. Even Mathematics, Natural Philosophy, and Natural Religion, are in some measure dependent on the science of MAN; since they lie under the cognizance of men, and are judg'd of by their powers and faculties ⁶.

At the time, the term natural philosophy referred to what we now call the natural sciences.

From man, our inquiry is directed more precisely to the faculty that judges: the understanding.

Hume follows a path already blazed a generation earlier by Locke in An Essay Concerning Human Understanding. Here is how he justifies this approach:

’Tis impossible to tell what changes and improvements we might make in these sciences were we thoroughly acquainted with the extent and force of human understanding, and cou'd explain the nature of the ideas we employ, and of the operations we perform in our reasonings. ⁷.

While this inquiry may benefit sciences that deal with objects having only a remote relation to man—such as mathematics, natural philosophy, or natural religion—it will be even more valuable to sciences whose object is man himself, such as logic, morals, criticism (or aesthetics), and politics. These four sciences comprehend almost every thing, which it can any way import us to be acquainted with ⁸.

Since there is not question of importance, whose decision is not compriz'd in the science of man; and there is none, which can be decided with any certainty, before we become acquainted with that science, human nature is the only true and solid foundation of our knowledge. In pretending therefore to explain the principles of human nature, we in effect propose a compleat system of the sciences, built on a foundation almost entirely new, and the only one upon which they can stand with any security ⁹.

The method for such a fundamental science: experience and observation. Here, Hume asserts his empiricism, which would later establish him as one of the leading figures of this philosophical school: And as the science of man is the only solid foundation for the other sciences, so the only solid foundation we can give to this science itself must be laid on experience and observation ¹⁰.

Hume acknowledges his predecessors—those have begun to put the science of man on a new footing ¹¹. Yet, he explicitly names only Bacon, referring to Locke in a more oblique manner: Some late other philosophers in England, an honour to our native country ¹².

Naturally, he does not merely rely on the argument from authority by invoking these great minds; he also legitimises the choice of the experimental method:

To me it seems evident, that the essence of the mind being equally unknown to us with that of external bodies, it must be equally impossible to form any notion of its powers and qualities otherwise than from careful and exact experiments, and the observation of those particular effects, which result from its different circumstances and situations.

And tho' we must endeavour to render all our principles as universal as possible, by tracing up our experiments to the utmost, and explaining all effects from the simplest and fewest causes, ’tis still certain we cannot go beyond experience; and any hypothesis, that pretends to discover the ultimate original qualities of human nature, ought at first to be rejected as presumptuous and chimerical ¹³.

"We cannot go beyond experience": here, then, is the founding principle of empiricism stated with absolute clarity—one that would provoke many reactions, particularly from Kant, who both adopted it and sought to transcend it in the Critique of Pure Reason.

Hume concludes the Introduction by acknowledging a difficulty: in the realm of morality, the experimental method cannot be applied in the same way. After all, one cannot kill a person simply to demonstrate the immoral nature of murder. In such cases, Hume even advocates recourse to indirect experience, relying on a cautious observation of human life [...] in the common course of the world, by men's behaviour in company, in affairs, and in their pleasures ¹⁴. By collecting and comparing such observations, we may hope to see the emergence of a moral science—one more useful than any other discipline.

¹ A Treatise of Human Nature, Oxford University Press, 2007, Volume 1, Introduction, p.3
² Ibid.
³ Ibid.
⁴ Ibid.
⁵ Critique of Pure Reason, Cambridge University Press, Cambridge, 1998, Preface, p.99
⁶ A Treatise of Human Nature, Introduction, p.4
⁷ Ibid.
⁸ Ibid.
⁹ Ibid.
¹⁰ Ibid.
¹¹ P.5
¹¹ Ibid.
¹² Ibid.
¹³ Ibid.
¹⁴ p.6