Philosophy of David Hume

General Notions

John Locke had determined the fundamental principle of Empiricism: the immediate object of knowledge is sensations which the subject experiences within himself.

From this doctrine arose the problem of determining whether outside these subjective representations there was a reality corresponding to them, and whether this reality was knowable.

Locke, with some hesitation making use of the principle of causality, had concluded affirmatively, by admitting the existence of substance as a support of such sensations, and the existence of God.

George Berkeley, another leading empiricist, had attacked the distinction between material and spiritual substance, and had denied the existence of the first, which he reduced to a mode of sensation. He had, however, affirmed the existence of spiritual substances, God and spirits.

Hume accepted dogmatically what had been the initial step for Locke and Berkeley -- namely, that the object of knowledge is solely the sense impressions perceived by the subject. But he did not allow himself to make any concession to classical philosophy, as Locke had done by admitting the validity of the principle of causality and the existence of substance. Nor was he guided by any dogmatic or religious principles, such as those which had led Berkeley to admit the existence of spiritual substance. Instead, Hume logically developed to its extreme conclusions the empiristic principle that subjective impressions alone are the immediate objects of knowledge. Passage outside our sensitive impressions is not possible. Hence there is no metaphysics: we know nothing of God, of the exterior world, or of our own soul.

Life and Works

David Hume was born in Edinburgh, Scotland, in 1711. He studied at the University in his native city, revealing a passionate interest in philosophy and literature. During a sojourn in France, he wrote his Treatise on Human Nature, in three volumes, which were published in 1739 and 1740. When this work did not meet with the success its author expected, Hume rewrote it in a more popular form, which he published successively under the titles Inquiry Concerning Human Understanding and Inquiry Concerning the Principles of Morals.

As a staff member of the British embassy, he had occasion to travel in Holland, Austria, Italy, and again in France. Here he struck up a friendship with Rousseau, whom he brought to England; but there this friendship was broken. Hume also dedicated himself to the study of history, and wrote an important History of Great Britain. He died in 1776. Besides the works already mentioned, other important ones by Hume are: Natural History of Religion, and Dialogues Concerning Natural Religion. Hume is a representative British type: litterateur, philosopher, politician, man of affairs and of the world.

Hume's Theory of Knowledge

According to Hume, the prime, constitutive and fundamental elements of knowledge are impressions and ideas. The difference between impressions and ideas lies in the degree of vividness with which the sensory fact is presented.

Thus the impression is an actual vivid perception which, as Hume says, brings with it conviction or positive belief in the existence of a corresponding objective reality. The idea is an element derived from the impression, and hence is less vivid than the latter; it is a copy which the impression leaves behind. It is one thing to open my eyes and see the red tapestry in the room where I am sitting, the table on which I am writing, and the objects which are on that table. It is another thing to close my eyes and have the image of what I have seen in my room. The first is impression, because it is vivid; the second is a weak representation of the first and is an idea.

Impressions and ideas are not psychic atoms isolated from one another. They are all linked together by an inclination to recall one another. This permits thought to pass from an actual impression to the idea of other impressions obtained in the past, and from these ideas to other ideas. This is the law of association of ideas, a fundamental point in Hume's doctrine and the basis for complex ideas. Thus ideas are naturally associated with one another and form large groups, and these groups in turn are related, to form still larger groups. The belief that behind these groups of representations there is a reality corresponding to them gives origin to belief in an external world, regulated by the same laws that exist in the world of thought. Hume distinguishes three type types of association: likeness, contiguity in time and space, cause and effect.

Another fundamental law of Hume's theory of knowledge is that of habit. Impressions succeed one another with a certain constancy. For example, every time I have drawn near the stove, I have felt warm. This realization, experienced in the past, of having observed one phenomenon constantly united with another, gives rise to the habit of my expecting also in the future a repetition of what has happened in the past, so that, having placed the first condition, I have a trusting expectancy of the second: every time I approach the stove, from force of habit I expect to warm myself. Force of habit gives to the constancy of the phenomenon experienced in the past the force of metaphysical necessity, and from it results the concept of substance, of the laws which govern such substances; in short, the resulting term is philosophy and science. But are philosophy and science reasonably justifiable? Hume answers in the negative.

How much absolute certainty are we able to attain? Hume admits only two instances:

• The certainty found in factual things, when we limit ourselves to the verification and description of facts expressed by actual past or present sensation (and disregard those which will be presented in the future). Thus an object is seen next to another, or after another; and these spatial and temporal relationships included in the impression are certain. I am likewise certain that some given impressions have been constantly co-related in the past -- for example, when one ball struck another, this latter moved.

• The certainty found in the relationships between ideas; for if we assume that ideas retain their identity, the relationships between them will be constant. On these relationships depend the universality and necessity of mathematical demonstrations, which show us the relations between ideas that are immutable in the abstract -- ideas whose logical value does not depend on the objects that correspond to them.

Outside these two types, there is no certitude, philosophical or scientific, strong enough to excluded all doubt.

Negation of Metaphysics and Science

Hume's criticism aimed at the destruction of the concept of space and time, of material and spiritual substance, of the principle of causality -- all of which are essential to philosophy and science. Among Hume's criticisms the most famous (historically) is the critique of the principle of causality, which we may summarize as follows:

A. Criticism of the Concept of Cause and Effect

The principle of causality consists in a relationship of necessary connection between cause and effect, in virtue of which the one (effect) cannot be had without the presence of the other (cause). Hence the formulation of the principle of causality: "Everything that begins to exist must have a cause for its existence."

Now this principle, or this absolute necessity of connection between the effect and its cause, is anything but exempt from doubt. Analytical a priori reasoning is such that it implies a proposition whose predicate is derivable from the idea of the subject -- as in the example, "Three times five is equal to fifteen." Now, according to Hume, the mind can never find the effect by examination of the supposed cause; for the effect is totally different from the cause, and consequently can never be discovered in it.

Motion in the second billiard ball is a quite distinct event from motion in the first; nor is there anything in the one to suggest the motion of the other, without the assistance of observation and experience. No man could infer merely from the fluidity of water that it would suffocate him. All these observations are true in the empiristic position of Hume, in which any idea is simply a copy of sensation. Thus the idea of the motion of the first billiard ball does not contain anything to suggest the motion of the second, and the idea of water does not include a priori the fact that it would suffocate a man.

In this regard we must observe that in the philosophy of Aristotelian realism a proposition is called analytical a priori not only when the predicate is found by analysis of the subject, but also when the predicate and the subject, while remaining two distinct concepts, have a transcendental relation to each other, a relation which is known intuitively by the intellect. This is precisely the case with the principle of causality, in which the mind, in comprehending the concept of that which begins to exist, discerns a necessary relation to another object, which is both the cause and the rational explanation of the thing that at first did not exist and now begins to exist.

The necessary connection upon which the principle of causality is based is not demonstrable, according to Hume, even by experience. Any fact -- for example, the striking together of two billiard balls, or any other fact to which we apply the concept of causality -- indicates to us nothing else but the constancy of the contiguity and succession of the two objects. But the stable union does not show me a necessary connection between the two. In the supposition that it has been observed by me and others that fact B is constantly joined with its antecedent, A, this constant repetition does not authorize me to say that always in the future fact B must follow upon fact A, and that between the two there is a necessary bond.

Hume states: "The repetition of perfectly similar instances can never alone give rise to the original idea, different from what is to be found in any particular instance." (Treatise on Human Nature, I, xiv.) Not even our activity and the effect of the will upon the movements of our body and our spirit can give us the impression of causality: "No relationship is more inexplicable," Hume adds, "than that which exists between the faculties of though and the essence of matter."

Here the Cartesian questions concerning the interplay between "res extensa" and "res cogitans" give Hume good arguments for denying the stability of causality, even in the movements which proceed from our own selves. Thus it is necessary to give up attributing any objective value to the idea of cause.

But whence comes the idea of causality, which undeniably exists? Hume answers that it arises from a psychological fact formed in the following manner.

• Experience has shown that fact B has constantly followed fact A.

• This stability, never contradicted by experience, shows indeed that the two facts, A and B, are associated with one another, so that the one evokes the other.

• Through force of association there arises in me the trusting expectation, and hence the habit of expecting, that also in the future, and necessarily, granted fact A, fact B must follow.

• Thus the necessary connection is not a bond which regulates reality, but is a manner of feeling on the part of the subject, a new law which the subject places in regard to his impressions.

B. Criticism of the Concept of Substance

An irresistible and universal conviction brings men to believe in a world of beings separate and distinct from the subject. Is such a conviction rationally justified?

Hume answers in the negative. If the immediate object of our knowledge is impressions, there is nothing in them to justify the affirmation that outside these impressions there are actual beings corresponding to them. In truth, if, as Hume holds, the impression is nothing other than a manner of feeling on the part of the subject, it is not possible for thought to go out of itself. Nor is recourse to the principle of causality valid (as Locke and Berkeley held); for we have seen that this principle, as far as Hume is concerned, has only a psychological value.

How then explain the idea of a world of beings separate and distinct from the subject -- a conviction which everyone holds? What is the origin of this belief? Hume gives the following explanation.

Many impressions, although intermittent and hence separable and distinct, are presented as being constantly similar. By the law of association these impressions evoke one another. Thought, in order to give itself an explanation of this stability, is brought to believe that these impressions are identical, and that hence, beneath them, there is some unchanging principle which gives unity to the sensible data that appear to be the same in impressions. Thus arises the concept of duality of subject and object, and, furthermore, the concept of substance as the support of impressions.

I open my eyes, and I see the objects disposed in a certain manner in my room. I go out, and after a time re-enter. The impressions which I receive of the position of those objects are entirely similar to the preceding ones, and the same will happen if I repeat the experience. These intermittent impressions are distinct, but they are similar and recall one another to mind. Thought, in order to give itself a reason why this can happen, is forced to admit the existence of some stable objective thing which is the support or basis of these similar impressions. Consequently, this concept of substance as the stable support of impressions, is not real, and is reduced to a fiction of the subject, originating in the constancy of similar impressions.

Hume's destructive criticism of the concept of material substance is also applied to spiritual substance, the personal ego. The idea we have of a personal ego ("anima") is not given by any impression, and hence is fictitious. Its origin is due to the behavior of the impressions themselves. We can affirm only the succession of impressions which, through the law of association, are gathered together into ever larger groups. Thought is then induced to conjure up a subject which unites all these groups; thoughts may be likened to a stage on which the impressions follow upon and recall one another. Hence comes the idea of the personal ego, of the spiritual soul, which the Cartesians accepted as the "primum notum." But not only is this ego nonexistent; it is one of the many fictions of thought advanced as a means of understanding impressions.

Thus Hume arrives at the denial of all the basic concepts of scientific and philosophical knowledge. So-called material and spiritual substances are only aggregations of impressions and ideas. The most basic principles, such as the principle of cause and effect, are reduced to psychological fictions, which are explained through the mechanism of association and habit. Hume, better than Berkeley, can say: "Omne esse est percipi" -- being is a mode of feeling.

Theoretical empirical reason concludes with the collapse of all rational understanding; it leads inevitably to Skepticism.

Religion and Ethics

Granted the failure of theoretical reason, it is no longer possible to prove the existence of God and hence the necessity of religion. Still, Hume does not deny the existence of God. In the light of reason, however, the existence of God is only a hypothesis and does not surpass the value of other hypotheses. Nor can religion be justified from the rational standpoint.

Hume defends a natural religion which owes its being to practical motives: Sentiments of terror and the need for protection in the face of the disturbing events of life and of nature push man to belief in a being (God) endowed with superior powers. Such sentiments carried primitive man to anthropomorphism, then to polytheism, and finally to monotheism. Monotheism corresponds better to intellectual exigencies, although man, because of practical necessities, never succeeds in freeing himself from the idea of polytheism.

The fact of moral obligation also arises from motives of practicality. Hume does not deny the distinction between the just and unjust as a datum of fact. But according to him, if the reasons which have given origin to this distinction are thoroughly examined, one comes to the conclusion that morality is the result of the sentiment of sympathy. According to this position, man approves certain actions of others as if they were his own, and approves of some of his own actions because he believes that by these actions he will meet with the approval of others.

Hume, lacking a metaphysics, had recourse to practical exigencies in order to justify the value of ethics, and of religion as well. This distinction between the theoretical and practical motives, and the justification of insuppressible values through practical motives alone, were to pass as a heritage to Immanuel Kant, and to form one of the pillars of his critical philosophy.

In morals, Hume set up the public good as the standard of right and wrong, and assigns to feelings rather than to reason the task of applying this ethical norm.

In Summary

Hume holds that the only thing that can be said, with full certainty, to exist is our perceptions (impressions and ideas). In and among these perceptions there is no causal connection; indeed, there is no knowable causality anywhere. If things outside us really do exist, there is no proof of their existence available to us.

David Hume is both an epistemological and metaphysical Subjectivist and a moral and ethical Relativist. His theories make both philosophical knowledge and scientific knowledge impossible. This is, of course, intellectual insanity of the worst sort.

Hume's vague philosophy has a very modern sound: a collection of impressions collected nowhere; contents of a mind which is not a container. Here we have the smug unintelligibility of the modern antirealist's definition of mind as "a cross-section of the environment."