Choosing what we mean by "causation" in the law.

• Author: Stapleton, Jane
• Position: Symposium: A Tribute to Professor David Fischer

In a radical new account of "causation" in the Law, I argue that "causation" is a term we use to express diverse information about the world. Clarity is promoted if we use the term "causation" to refer to the information yielded by only one type of inquiry. Lawyers have used the term to refer to more than one type of enquiry, and philosophers often do not specify an inquiry. The most useful inquiry for legal purposes is one that compares the actual world of a particular phenomenon with a hypothetical world and thereby determines, in the context of that comparison, the role that a specified factor played, if any, in the existence of the actual phenomenon. It is convenient to separate three forms of such a role of "involvement": necessity, duplicate necessity and contribution, though contribution subsumes the others. We use our knowledge of the physical laws of nature, evidence of behaviour and so on to distinguish involved factors from factors that are merely "associated" with that phenomenon by a relation of constant conjunction: a determination that can be done objectively. I argue that Law should unequivocally choose involvement as the interrogation underlying causal terminology because (a) it promotes clarity and avoids ambiguity; (b) it promotes the clear identification of normative issues and provides a more transparent distribution of issues between "causation" and other analytical elements within legal analysis; and (c) it best serves the Law's very wide range of purposes.

Part I of this article sets out the above argument. Part II sketches the approach of others to the issue of "causation in the Law."

1. INVOLVEMENT

   1. General Laws

      The world is out there, seamless and rolling along, manifesting what we call the physical laws of nature in complex confluence and combinations. Just as we can deconstruct a particular Van Gogh painting we admire into the three primary colours, so too we can use a variety of limited interrogations to investigate this complex world and discover its underlying building blocks of physical laws. (1) A well-known example is Newton's First Law of Motion: in an isolated system, an object will maintain a constant velocity unless acted upon by an unbalanced force.

      We express this latter proposition as a "law" to indicate that it applies (or so it seems on the non-quantum scale) in our natural world. Of course, we can imagine other worlds where this proposition does not hold because, for example, miracles happen or witches cast spells, and we can acknowledge that we do not know why it holds in our natural world, (2) but these possibilities are not the concern of lawyers who are only concerned with our natural world and hypothetical variants of it in which such physical principles hold.

      So if we call "medium necessity" the relation that in our natural world (and the hypothetical variants of it in which lawyers are interested) if A does not occur, B also does not occur, (3) Newton's First Law of Motion can be expressed in such terms: in all possible relevant variants of our natural world in which an object has not been acted upon by an unbalanced force, deviation from constant velocity does not occur; or, in all possible relevant variants of our natural world, absence of an unbalanced force is "necessary" for an object to maintain constant velocity. We can also state the First Law in terms of "medium sufficiency": in all possible relevant variants of our natural world, that Y did not occur entails that X did not occur. For example: in all possible relevant variants of our natural world, that deviation from constant velocity did not occur entails (i.e. is sufficient to establish the truth of the proposition) that the object had not been acted upon by an unbalanced force.

   2. Individual Phenomena and Specified Factors

      Armed with such knowledge of general physical laws and other data such as eyewitness testimony of behaviour, we can investigate a particular individual phenomenon. This phenomenon might, for example, be the actual persistence of a specified state (the cannonball resting on Kant's cushion) or the actual transition from a specified state to another (the fall of the apple from the tree onto Newton's head).

      Typically our investigations into a particular phenomenon focus on a specified factor--such as a physical force, the absence of something (4) or a specific piece of communicated information. Importantly in the particular context of the Law, the specification of the factor is precise and often arises from what the Law has mandated: if the Law had mandated that Newton's mother should hold an umbrella above her son's head and Mrs. Newton omitted to do this, one factor of interest would be this absence, specified as "Mrs. Newton's omission to hold the umbrella as mandated."

      Often we are interested to compare the actual world of the particular phenomenon (which, of course, includes our specified factor) with a hypothetical world (which we construct by notionally omitting the specified factor and sometimes other factors). By doing this we can then determine, in the context of that comparison, the role the specified factor played, if any, in the existence of the actual phenomenon. Importantly in the particular context of the Law, there is often need to consider a hypothetical world, which not only never existed, (5) but which also is one which in retrospect is known could not have existed. An example of such a world is one in which a retailer would have made a $30 profit from a farmer fulfilling a contractual promise to deliver peas on a certain day ... a delivery which turned out to be impossible; in the context of that comparison it is important to understand how it is that lawyers convey meaningful information when they say that the farmer's contractual breach "caused" the retailer to suffer a $30 "loss" (see below). (6)

      As to the role the specified factor may have played in the existence of the actual phenomenon, it is convenient to separate three forms of role which collectively I call "involvement" in order to avoid circular causal terminology: necessity, duplicate necessity and contribution (though, strictly, contribution subsumes the others, see below). For example, one hypothetical world we might consider is one identical to the actual world except that the specified factor is absent from it. If, by applying our data such as the physical laws of nature, we are confident that in this hypothetical world the particular phenomenon would not have occurred, we can express this information by saying that the specified factor was involved in the existence of the actual phenomenon by being "necessary" for it. (7)

      To illustrate: suppose Michael's gardener had undertaken a contractual obligation to Michael to provide a certain amount of artificial watering to Michael's plant (e.g. two litres per day). In the actual world the gardener fails to provide any water to the plant, even though he could easily have done so; (8) and the plant dies. When Michael sues his gardener for breach of contract: the specific factor of interest to the Law will be the omission by the gardener to water the plant with two litres per day; the particular phenomenon of interest, the one about which Michael is complaining, will be the (actual transition to) the death of the plant; and Michael will only recover compensation from the gardener for the plant's death if the specified factor played some role in that death, for example by being necessary.

      To determine whether the gardener's omission was involved in the plant's death by being necessary, the Law can consider, using our understanding of the physical laws of nature and so on, what the fate of the plant would have been in the absence of ("but-for") the specified factor: namely, a hypothetical world in which the gardener did provide the relevant contracted-for amount of artificial watering to Michael's plants. First, suppose that the plant would have flourished had it received that amount of water: (9) we can express this information by saying that the gardener's breach of contract was involved in the actual death of the plant, specifically by being necessary. (10) Conversely, suppose the plant would still have died in the same way, time and place had it received the mandated amount of water: again, we can express this information by saying that the gardener's breach of contract was not involved in that death, at least not in the sense of being necessary for it. (11) Note that the information conveyed by the notion of "involvement" is context-specific: it depends, for example, on the specification of the particular phenomenon of interest and the specification of the factor of interest.

      As to the data on which we draw to identify a factor's "involvement" in the particular phenomenon, these include evidence of behaviour and our knowledge of the physical laws of nature, such as Newton's First Law, which allow us to distinguish between a lawful regularity manifesting the physical laws of nature and the law-like regularity of a mere association such as the epiphenomenal fall of a barometer before a storm. (12)

   3. The Variety of Interrogations into a Particular Phenomenon

      When we investigate whether a specified factor was involved in the existence of the particular phenomenon, we can use a variety of interrogations ranging from the broadest--was the factor involved in any way?--to much narrower interrogations such as explanation or blame. Importantly, these different interrogations yield different sorts of information. For example, (13) take the case where: due to the carelessness of each of two unrelated hunters, a mountain walker is simultaneously shot by both and the medical evidence is clear that either shot would have been sufficient to result in instantaneous death; and a hunting official who had contractually promised the hunters to shout them a warning about the presence of any walkers had remained silent even though he had seen the mountain...