has a right to life. For this requirement, when taken together with the claim that there is at least one property, possessed by adult humans, such that any organism possessing it has a serious right to life, entails the denial of the potentiality principle. Or at least this is so if we add the uncontroversial empirical claim that an organism that will in the normal course of events develop into an adult human does not from the very beginning of its existence possess a concept of a continuing subject of experiences together with a belief that it is itself such an entity.
I think it best, however, to scrutinize the potentiality principle itself, and not to base one’s case against it simply on the self‐consciousness requirement. Perhaps the first point to note is that the potentiality principle should not be confused with principles such as the following: the value of an object is related to the value of the things into which it can develop. This “valuation principle” is rather vague. There are ways of making it more precise, but we need not consider these here. Suppose now that one were to speak not of a right to life, but of the value of life. It would then be easy to make the mistake of thinking that the valuation principle was relevant to the potentiality principle – indeed, that it entailed it. But an individual’s right to life is not based on the value of his life. To say that the world would be better off if it contained fewer people is not to say that it would be right to achieve such a better world by killing some of the present inhabitants. If having a right to life were a matter of a thing’s value, then a thing’s potentialities, being connected with its expected value, would clearly be relevant to the question of what rights it had. Conversely, once one realizes that a thing’s rights are not a matter of its value, I think it becomes clear that an organism’s potentialities are irrelevant to the question of whether it has a right to life.
But let us now turn to the task of finding a direct refutation of the potentiality principle. The basic issue is this. Is there any property J which satisfies the following conditions: (1) There is a property K such that any individual possessing property K has a right to life, and there is a scientific law L to the effect that any organism possessing property J will in the normal course of events come to possess property K at some later time. (2) Given the relationship between property J and property K just described, anything possessing property J has a right to life. (3) If property J were not related to property K in the way indicated, it would not be the case that anything possessing property J thereby had a right to life. In short, the question is whether there is a property J that bestows a right to life on an organism only because J stands in a certain causal relationship to a second property K, which is such that anything possessing that property ipso facto has a right to life.
My argument turns upon the following critical principle: Let C be a causal process that normally leads to outcome E. Let A be an action that initiates process C, and B be an action involving a minimal expenditure of energy that stops process C before outcome E occurs. Assume further that actions A and B do not have any other consequences, and that E is the only morally significant outcome of process C. Then there is no moral difference between intentionally performing action B and intentionally refraining from performing action A, assuming identical motivation in both cases. This principle, which I shall refer to as the moral symmetry principle with respect to action and inaction, would be rejected by some philosophers. They would argue that there is an important distinction to be drawn between “what we owe people in the form of aid and what we owe them in the way of non‐interference,”25 and that the latter, “negative duties,” are duties that it is more serious to neglect than the former, “positive” ones. This view arises from an intuitive response to examples such as the following. Even if it is wrong not to send food to starving people in other parts of the world, it is more wrong still to kill someone. And isn’t the conclusion, then, that one’s obligation to refrain from killing someone is a more serious obligation than one’s obligation to save lives?
I want to argue that this is not the correct conclusion. I think it is tempting to draw this conclusion if one fails to consider the motivation that is likely to be associated with the respective actions. If someone performs an action he knows will kill someone else, this will usually be grounds for concluding that he wanted to kill the person in question. In contrast, failing to help someone may indicate only apathy, laziness, selfishness, or an amoral outlook: the fact that a person knowingly allows another to die will not normally be grounds for concluding that he desired that person’s death. Someone who knowingly kills another is more likely to be seriously defective from a moral point of view than someone who fails to save another’s life.
If we are not to be led to false conclusions by our intuitions about certain cases, we must explicitly assume identical motivations in the two situations. Compare, for example, the following: (1) Jones sees that Smith will be killed by a bomb unless he warns him. Jones’s reaction is: “How lucky, it will save me the trouble of killing Smith myself.” So Jones allows Smith to be killed by the bomb, even though he could easily have warned him. (2) Jones wants Smith dead, and therefore shoots him. Is one to say there is a significant difference between the wrongness of Jones’s behavior in these two cases? Surely not. This shows the mistake of drawing a distinction between positive duties and negative duties and holding that the latter impose stricter obligations than the former. The difference in our intuitions about situations that involve giving aid to others and corresponding situations that involve not interfering with others is to be explained by reference to probable differences in the motivations operating in the two situations, and not by reference to a distinction between positive and negative duties. For once it is specified that the motivation is the same in the two situations, we realize that inaction is as wrong in the one case as action is in the other.
There is another point that may be relevant. Action involves effort, while inaction usually does not. It usually does not require any effort on my part to refrain from killing someone, but saving someone’s life will require an expenditure of energy. One must then ask how large a sacrifice a person is morally required to make to save the life of another. If the sacrifice of time and energy is quite large it may be that one is not morally obliged to save the life of another in that situation. Superficial reflection upon such cases might easily lead us to introduce the distinction between positive and negative duties, but again it is clear that this would be a mistake. The point is not that one has a greater duty to refrain from killing others than to perform positive actions that will save them. It is rather that positive actions require effort, and this means that in deciding what to do a person has to take into account his own right to do what he wants with his life, and not only the other person’s right to life. To avoid this confusion, we should confine ourselves to comparisons between situations in which the positive action involves minimal effort.
The moral symmetry principle, as formulated above, explicitly takes these two factors into account. It applies only to pairs of situations in which the motivations are identical and the positive action involves minimal effort. Without these restrictions, the principle would be open to serious objection; with them, it seems perfectly acceptable. For the central objection to it rests on the claim that we must distinguish positive from negative duties and recognize that negative duties impose stronger obligations than positive ones. I have tried to show how this claim derives from an unsound account of our moral intuitions about certain situations.
My argument against the potentiality principle can now be stated. Suppose at some future time a chemical were to be discovered which when injected into the brain of a kitten would cause the kitten to develop into a cat possessing a brain of the sort possessed by humans, and consequently into a cat having all the psychological capabilities characteristic of adult humans. Such cats would be able to think, to use language, and so on. Now it would surely be morally indefensible in such a situation to ascribe a serious right to life to members of the species Homo sapiens without also ascribing it to cats that have undergone such a process of development: there would be no morally significant differences.
Secondly, it would not be seriously wrong to refrain from injecting a newborn kitten with the special chemical, and to kill it instead. The fact that one could initiate a causal process that would transform a kitten into an entity that would eventually possess properties such that anything possessing them ipso facto has a serious right to life does not mean