Broad wrote an influential essay on Libertarianism in 1952 that introduced the confusing philosophical jargon terms "occurrent causation" and "non-occurrent causation," which became the basis for today's "agent causal" and "event causal" distinctions.

This is sadly typical of analytical language philosophers, who hope to clarify our use of ordinary language in philosophy but often abuse language and confuse things instead. Broad believes that his "non-occurrent causation" does occur.

Broad considered the "putting forth of a certain amount of effort" by an individual to be

"literally determined by the agent or self, considered as a substance or continuant, and not by a total cause which contains as factors events in and dispositions of the agent. If this could be maintained, our puttings-forth of effort would be completely determined, but their causes would neither be events nor contain events as cause-factors. Certain series of events would then originate from causal progenitors which are continuants and not events. Since the first event in such a series would be completely determined, it would not be an accident. And, since the total cause of such an event would not be an event and would not contain an event as a cause-factor, the two alternatives 'completely determined' and 'partially undetermined' would both be inapplicable to it. For these alternatives apply only to events."

"Let us call the kind of causation which I have just described... 'non-occurrent causation of events.' We will call the ordinary kind of causation, which I had in mind when I defined 'Determinism' and 'Indeterminism,' 'occurrent causation.'"

Broad also used the ambiguous term "causal progenitor" to describe the beginning of a new causal chain - a causa sui or uncaused cause. Originator would have been better. He says such a cause is neither 'completely determined' nor 'partially undetermined.'

"Certain series of events would then originate from causal progenitors which are continuants and not events. Since the first event in such a series would be completely determined, it would not be an accident. And, since the total cause of such an event would not be an event and would not contain an event as a cause-factor, the two alternatives 'completely determined' and 'partially undetermined' would both be inapplicable to it. For these alternatives apply only to events."

Broad found Indeterminism to be possible, but Libertarianism, which according to his definition entails Indeterminism, he found to be impossible.

"We are now in a position to define what I will call 'Libertarianism.' This doctrine may be summed up in two propositions. (i) Some (and it may be all) voluntary actions have a causal ancestor which contains as a cause-factor the putting-forth of an effort which is not completely determined in direction and intensity by occurrent causation. (ii) In such cases the direction and the intensity of the effort are completely determined by non-occurrent causation, in which the self or agent, taken as a substance or continuant, is the non-occurrent total cause. Thus, Libertarianism, as defined by me, entails Indeterminism, as defined by me; but the converse does not hold."

If I am right, Libertarianism is self-evidently impossible, whilst Indeterminism is prima facie possible.

Ethics and the History of Philosophy. London: Routledge & Kegan Paul, 1952, pp. 195-217.

The Implications of Obligability

We often make retrospective judgments about the past actions of ourselves or other people which take the form: 'You ought not to have done the action X, which you in fact did; you ought instead to have done the action Y, which in fact you did not.' If I make such a judgment about a person, and he wants to refute it, he can take two different lines of argument. (1) He may say: 'I could have done Y instead of X, but you are mistaken in thinking that Y was the action that I ought to have done. In point of fact, X, the action that I did, was the one that I ought to have done. If I had done Y, I should have done what I ought not to have done.' (2) He may say: 'I could not help doing X,' or he may say: 'Though I need not have done X, I could not possibly have done Y.'

If the accused person makes an answer of the first kind, he is admitting that the alternatives 'ought' and 'ought not' apply to the actions X and Y, but he is objecting to my applying 'ought' to Y and 'ought not' to X. He is saying that 'ought' applies to X, and 'ought not' to Y. It is as if two people, who agree that X and Y are each either black or white, should differ because one holds that X is black and Y white whilst the other holds that X is white and Y black. If the accused person makes an answer of the second kind, he is denying the applicability of the alternatives 'ought' and 'ought not.' If he says: 'I could not help doing X,' he assumes that his critic will admit that neither 'ought' nor 'ought not' has any application to an action which the agent could not help doing. If he says: 'Though I need not have done X, yet I could not possibly have done Y,' he assumes that his critic will admit that neither 'ought' nor `ought not' has any application to an action which the agent could not have done. It is as if one person should say that X is black and Y is white, and the other should answer that at least one of them is unextended and therefore incapable 'of being either black or white...

Analysis of Categorical Substitutability

We can now proceed to discuss the notion of categorical substitutability. It seems to me to involve a negative and a positive condition. I think that the negative condition can be clearly formulated, and that there is no insuperable difficulty in admitting that it may sometimes be fulfilled. The ultimate difficulty is to give any intelligible account of the positive condition. I will now explain and illustrate these statements.

Suppose that, on a certain occasion, I willed a certain alternative with a certain degree of force and persistence, and that, in consequence of this volition, I did a certain voluntary action which I should not have done unless I had willed this alternative with this degree of intensity and persistence. To say that I categorically could have avoided doing this action implies at least that the following negative condition is fulfilled. It implies that the process of my willing this alternative with this degree of force and persistence was not completely determined by the nomic, the occurrent, the dispositional, and the background conditions which existed immediately before and during this process of willing. In order to see exactly what this means it will be best to contrast it with a case in which we believe that a process is completely determined by such conditions.

Suppose that two billiard-balls are moving on a table, that they collide at a certain moment, and that they go on moving in modified directions with modified velocities in consequence of the impact.

Let us take as universal premisses the general laws of motion and of elastic impact. We will call these 'nomic premisses.' Let us take as singular premisses the following propositions. (i) That each ball was moving in such and such a direction and with such and such a velocity at the moment of impact. We will call this an 'occurrent premiss.' (ii) That the masses and co-efficients of elasticity of the balls were such and such. We will call this a `dispositional premiss.' (iii) That the table was smooth and level before, at, and after the moment of impact. We will call this a 'background premiss.' Lastly, let us take the proposition that the balls are moving, directly after the impact, in such and such directions with such and such velocities. Then this last proposition is a logical consequence of the conjunction of the nomic, the occurrent, the dispositional, and the background premisses. That is to say, the combination of these premisses with the denial of the last proposition would be logically inconsistent. It is so in exactly the sense in which the combination of the premisses of a valid syllogism with the denial of its conclusion would be so.

The Negative Condition

We can now work towards a definition of the statement that a certain event e was completely determined in respect of a certain characteristic. When we have defined this statement it will be easy to define the statement that a certain event was not completely determined in respect of a certain characteristic...

We can now define the statement that a certain event e was completely determined. It means that e has zero range of indetermination for every dimension of every determinable characteristic of which it is a manifestation. The statement that a certain event e was not completely determined can now be defined. It means that e had a finite range of indetermination for at least one dimension of at least one of the characteristics of which it was a manifestation.

And now at last we can define 'Determinism' and 'Indeterminism.' Determinism is the doctrine that every event is completely determined, in the sense just defined. Indeterminism, is the doctrine that some, and it may be all, events are not completely determined, in the sense defined. Both doctrines are, prima facie, intelligible, when defined as I have defined them.

There is one other point to be noticed. An event might be completely determined, and yet it might have a 'causal ancestor' which was not completely determined. If Y is the total cause of Z, and X is the total cause of Y, I call both Y and X 'causal ancestors' of Z. Similarly, if W were the total cause of X, I should call Y, X, and W 'causal ancestors' of Z. And so on. If at any stage in such a series there is a term, e.g. W, which contains a cause-factor that is not completely determined, the series will stop there, just as the series of human ancestors stops with Adam. Such a term may be called the 'causal progenitor' of such a series. If Determinism be true, every event has causal ancestors, and therefore there are no causal progenitors. If Indeterminism be true, there are causal progenitors in the history of the world.

The Positive Condition

Let us now try to discover the positive conditions of categorical obligability. I think that we should naturally tend to answer the sort of objection which I have just raised in the following way. We should say: 'I deliberately identified myself with my desire to do A, or I deliberately threw my weight on the side of that desire. I might instead have made no particular effort in one direction or the other; or I might have identified myself with, and thrown my weight on the side of, my desire to do B. So my desire to do A did not just happen to be present with the requisite strength and persistence, as compared with my desire to do B. It had this degree of strength and persistence because, and only because, I reinforced it by a deliberate effort, which I need not have made at all and which I could have made in favour of my desire to do B.' Another way of expressing the same thing would be this: 'I forced myself to do A; but I need not have done so, and, if I had not done so, I should have done B.' Or again: 'I might have forced myself to do B; but I did not, and so I did A.'

It is quite plain that these phrases express a genuine positive experience with which we are all perfectly familiar. They are all, of course, metaphorical. It will be noticed that they all attempt to describe the generic fact by metaphors drawn from specific instances of it, e.g. deliberately pressing down one scale of a balance, deliberately joining one side in a tug-of-war, deliberately thrusting a body in a certain direction against obstacles, and so on. In this respect they may be compared with attempts to describe the generic facts about time and change by metaphors drawn from specific instances, such as flowing streams, moving spots of light, and so on. The only use of such metaphors is to direct attention to the sort of fact which one wants one's hearers to contemplate. They give no help towards analysing or comprehending this fact. A metaphor helps us to understand a fact only when it brings out an analogy with a fact of a different kind, which we already understand. When a generic fact can be described only by metaphors drawn from specific instances of itself it is a sign that the fact is unique and peculiar, like the fact of temporal succession and the change of events from futurity, through presentness, to pastness.

Granted that there is this unique and peculiar factor of deliberate effort or reinforcement, how far does the recognition of it help us in our present problem? So far as I can see, it merely takes the problem one step further back. My doing of A is completely determined by a total cause which contains as factors my desire to do A and my desire to do B, each of which has a certain determinate strength and persistence. The preponderance of my desire to do A over my desire to do B, in respect of strength and persistence, is completely determined by a total cause which contains as a factor my putting forth a certain amount of effort to reinforce my desire for A. This effort-factor is not completely determined. It is logically consistent with all the nomic, occurrent, dispositional, and background facts that no effort should have been made, or that it should have been directed towards reinforcing the desire for B instead of the desire for A, or that it should have been put forth more or less strongly than it actually was in favour of the desire for A. Surely then we can say no more than that it just happened to occur with a certain degree of intensity in favour of the desire for A.

I think that the safest course at this stage tor those who maintain that some actions are categorically obligable would be the following. They should admit quite frankly what I have just stated, and should then say: 'However paradoxical it may seem, we do regard ourselves and other people as morally responsible for accidents of this unique kind, and we do not regard them as morally responsible, in the categorical sense, for anything but such accidents and those consequences of them which would have been different if the accidents had happened differently. Only such accidents, and their causal descendants in the way of volition and action, are categorically obligable.' If anyone should take up this position, I should not know how to refute him, though I should be strongly inclined to think him mistaken.

This is not, however, the position which persons who hold that some actions are categorically obligable, generally do take at this point. I do not find that they ever state quite clearly what they think they believe, and I suspect that is because, if it were clearly stated, it would be seen to be impossible. I shall therefore try to state clearly what I think such people want to believe, and shall try to show that it is impossible. I suspect that they would quarrel with my statement that, on their view, the fact that one puts forth such and such an effort in support of a certain desire is, in the strictest sense, an accident. They would like to say that the putting forth of a certain amount of effort in a certain direction at a certain time is completely determined, but is determined in a unique and peculiar way.

It is literally determined by the agent or self, considered as a substance or continuant, and not by a total cause which contains as factors events in and dispositions of the agent. If this could be maintained, our puttings-forth of effort would be completely determined, but their causes would neither be events nor contain events as cause-factors. Certain series of events would then originate from causal progenitors which are continuants and not events. Since the first event in such a series would be completely determined, it would not be an accident. And, since the total cause of such an event would not be an event and would not contain an event as a cause-factor, the two alternatives 'completely determined' and 'partially undetermined' would both be inapplicable to it. For these alternatives apply only to events.

I am fairly sure that this is the kind of proposition which people who profess to believe in Free Will want to believe. I have, of course, stated it with a regrettable crudity, of which they would be incapable. Now it seems to me clear that such a view is impossible. The putting-forth of an effort of a certain intensity, in a certain direction, at a certain moment, for a certain duration, is quite clearly an event or process, however unique and peculiar it may be in other respects. It is therefore subject to any conditions which self-evidently apply to every event, as such. Now it is surely quite evident that, if the beginning of a certain process at a certain time is determined at all, its total cause must contain as an essential factor another event or process which enters into the moment from which the determined event or process issues. I see no prima facie objection to there being events that are not completely determined. But, in so far as an event is determined, an essential factor in its total cause must be other events. How could an event possibly be determined to happen at a certain date if its total cause contained no factor to which the notion of date has any application? And how can the notion of date have any application to anything that is not an event?

Of course I am well aware that we constantly use phrases, describing causal transactions, in which a continuant is named as the cause and no event in that continuant is mentioned. Thus we say: 'The stone broke the window,' 'The cat killed the mouse,' and so on. But it is quite evident that all such phrases are elliptical. The first, e.g., expresses what would be more fully expressed by the sentence: 'The coming in contact of the moving stone with the window at a certain moment caused a process of disintegration to begin in the window at that moment.' Thus the fact that we use and understand such phrases casts no doubt on the general principle which I have just enunciated.

Let us call the kind of causation which I have just described and rejected 'non-occurrent causation of events.' We will call the ordinary kind of causation, which I had in mind when I defined 'Determinism' and 'Indeterminism,' 'occurrent causation.'

Now I think we can plausibly suggest what may have made some people think they believe that puttings-forth of effort are events which are determined by non-occurrent causation. It is quite usual to say that a man's putting-forth of effort in a certain direction on a certain occasion was determined by 'Reason' or 'Principle' or 'Conscience' or 'The Moral Law.' Now these impressive names and phrases certainly do not denote events or even substances. If they denote anything, they stand for propositions or systems of propositions, or for those peculiar universals or systems of universals which Plato called 'Ideas.' If it were literally true that puttings-forth of effort are determined by such entities, we should have causation of events in time by timeless causes. But, of course, statements like 'Smith's putting-forth of effort in a certain direction on a certain occasion was determined by the Moral Law' cannot be taken literally. The Moral Law, as such, has no causal efficacy. What is meant is that Smith's belief that a certain alternative would be in accordance with the Moral Law, and his desire to do what is right, were cause-factors in the total cause which determined his putting-forth of effort on the side of that alternative. Now this belief was an event, which happened when he began to ;effect on the alternatives and to consider them in the light of the moral principles which he accepts and regards as relevant. And this desire was an event, which happened when his conative-emotional moral dispositions were stirred by the process of reflecting on the alternatives. Thus the use of phrases about action being 'determined by the Moral Law' may have made some people think they believe that some events are determined by non-occurrent causation. But our analysis of the meaning of such phrases shows that the facts which they express give no logical support to this belief.

Libertarianism

We are now in a position to define what I will call 'Libertarianism.' This doctrine may be summed up in two propositions. (i) Some (and it may be all) voluntary actions have a causal ancestor which contains as a cause-factor the putting-forth of an effort which is not completely determined in direction and intensity by occurrent causation. (ii) In such cases the direction and the intensity of the effort are completely determined by non-occurrent causation, in which the self or agent, taken as a substance or continuant, is the non-occurrent total cause. Thus, Libertarianism, as defined by me, entails Indeterminism, as defined by me; but the converse does not hold.

If I am right, Libertarianism is self-evidently impossible, whilst Indeterminism is prima facie possible. Hence, if categorical obligability entails Libertarianism, it is certain that no action can be categorically obligable. But if categorical obligability entails only Indeterminism, it is prima facie possible that some actions are categorically obligable. Unfortunately, it seems almost certain that categorical obligability entails more than Indeterminism, and it seems very likely that it entails Libertarianism. It is therefore highly probable that the notion of categorical obligability is a delusive notion, which neither has nor can have any application.