Conclusiones del tercer capítulo

With this discussion as a background, I will now examine, in detail, the central interventionist notion of invariance. According to interventionism, it is

invariance  that  is  “the  key  feature  a  relationship  must  possess  if  it  is  to  count  as   causal   or   explanatory”   (Woodward,   2003:   239)   and   hence   it   is   invariance that distinguishes genuinely causal from non-causal relationships. Moreover, as we shall see, invariance plays a central role in the argument against the SP concept of causation and in the interventionist account of mental causation outlined in the next chapter.

The basic idea of invariance is captured in the following passage:

“…if  a  causal  relationship  between  C and E holds at all, then it must be

true that (and the relationship must correctly describe how) for some interventions and background circumstances, E will change under those interventions on C. This in turn implies that there must be some relationship between C and E and some interventions on C such that if these were to be carried out, that relationship between C and E would not break down but rather would continue to hold. When this is true, I say that the relationship is invariant under such interventions and background circumstances. Thus, according to a manipulationist account of causation, if a relationship is to qualify as causal, it must be invariant under some

In other words, according to interventionism, if the relationship between two variables is genuinely causal, we should expect a certain degree of stability in the response of the effect to interventions on the purported cause variable. If no such stable response (to interventions) exists, then that relationship will fail to qualify as causal. For example, in order for it to be true that attendance at private school causes scholastic achievement, it must be true that the relationship between attendance and achievement is invariant, i.e. that it holds under at least some intervention on attendance. If this relationship fails to hold under any interventions on attendance, then the relationship will fail to be invariant and hence fail to qualify as causal.

Woodward provides the following precise definition of invariance:

“A  generalization  G (relating, say, changes in the value of X to changes in the value of Y) is invariant if G would continue to hold under some intervention that changes the value of X in such a way that, according to

G, the value of Y would change- ‘continue   to   hold’   in   the   sense   that  G

correctly describes how the value of Y would change under this intervention.”  (Ibid:  15)  

Now, as the passages above suggest, in order for a relationship or generalization to be invariant and hence causal according to interventionism, it is not necessary that that relationship is invariant under all changes and background conditions, but it is only necessary that it is invariant under a specific kind of change, namely an intervention.

The reason why it is invariance under interventions that takes a privileged role in determining whether X causes Y is simply because it is possible for mere correlations to remain invariant under some changes to background conditions.9

As an illustration, consider the following example (originally due to Lewis, 1973b): the relationship between a barometer reading, B, and the occurrence of a storm, S, is invariant under certain changes, for example, changes to whether it is a Tuesday, or a Wednesday, whether the barometer is in London or Beijing and so on. However, despite being invariant under these changes, it is clear that B does not cause S, since both B and S are joint effects of a common cause, namely atmospheric pressure. It is for this reason that Woodward stipulates that it is only invariance under interventions (and more specifically, invariance under interventions on the variables that feature in the generalization or claim itself) that are necessary for determining whether the relationship between X and Y is causal.10

As the passages above also suggest, in order for some relationship or generalization to qualify as invariant and hence causal, it is not necessary that that relationship is invariant across all interventions, but it is sufficient that it is invariant under at least some intervention. In other words, there is a threshold of

9 _{In Section 4.4 below, I discuss the interventionist notion of insensitivity, which}

does consider changes to background conditions as relevant for assessing the degree of insensitivity. 10 _{In fact, it is a specific}

kindof  intervention  on  those  variables,  namely  a  ‘testing  intervention’  

that is relevant for assessing invariance. Very roughly, the notion of a testing intervention captures the idea that interventions should test the discriminating features of a relationship, if they are to determine whether that relationship is causal. Consider the following example adapted from Woodward (2003: 248-249): imagine that a light is attached to a switch and consider the generalization that the light will remain off if the switch is in any position less than 57 degrees and will turn on if the switch is in any position greater than 57 degrees. In order to determine whether this relationship is causal, the intervention should change the discriminating feature of the switch, i.e. change the position of the switch from any position below 57 degrees to any position greater than 57 degrees. For the remainder of  Woodward’s  discussion,  he  simply  takes   the   term   ‘intervention’   to   refer   to   this   specific   kind   of   testing   intervention   and   I   follow  

invariance that a generalization or relationship must pass if it is to qualify as causal: those generalizations and relationships that are invariant under at least

some intervention will pass the threshold of invariance and hence qualify as

causal11_{, whereas those generalizations and relationships that are not invariant}

under any interventions will fail to pass the threshold of invariance and hence fail

to qualify as causal. This captures the intuitive idea that it is possible for X to cause Y even though it is not true that X causes Y in every situation and in all background conditions. Moreover, it also captures the idea that there is a minimal

degree of invariance that a relationship or generalization must possess if it is to qualify as causal. These points will be especially relevant to our later discussion.

As well as having a threshold, a feature of invariance that is also relevant to the discussion in the next chapter is that invariance comes in varying degrees. Significantly, it is the contrast between highly invariant generalizations and relationships, on the one hand, and relatively unstable generalizations and relationships, on the other, that tracks the difference between highly explanatory generalizations and relationships and relatively explanatorily shallow generalizations and relationships.12 The reason why highly invariant generalizations and relationships are also highly explanatory is fairly simple: by being invariant over a wide range of interventions, those generalizations and relationships will simply be able to answer a wider range of w-questions. Moreover, by being invariant over a wider range of changes, those relationships

11 _{In saying this I do not mean that X can cause Y even if there is only one single intervention on} X (that occurs just once, either hypothetically or actually and could never occur again) that changes Y, since it is built into the notion of invariance that if X causes Y, the invariant relationship between X and Y would be potentially reproducible in the sense that under this specific intervention, X would change Y.

12 _{The other feature of interventionism that also tracks the difference between}

better or worse causal claims and explanations, and which will be extremely relevant to the argument in this thesis, is the notion of contrastive focus, which I will discuss in detail later in this chapter and in the next.

and generalization will also be more potentially exploitable for the purposes of control and manipulation, in the sense that they will continue to hold and hence continue to provide a potential means of control, over a wide range of interventions.

By contrast, those generalizations and relationships that are less invariant will qualify as less explanatory, since by being invariant over a much more limited range of interventions, they will be able to answer a much more limited range of w-questions. Moreover, those relationships that display a relatively low degree of invariance, whilst allowing some measure of control and manipulation, will be less potentially useful since they will break down outside a narrow range of interventions. By way of further contrast, note that those relationships that fail to be invariant under any interventions and hence fail to qualify as causal, will not be potentially useful for the purposes of control and manipulation whatsoever, in line with the manipulationist account of causation outlined thus far.

The notion of invariance thus explains how certain generalizations and relationships can fail to qualify as causal and explanatory (by failing to pass the threshold of invariance), but also explains how generalizations and relationships that do pass this threshold (and hence qualify as causal) can come in varying

degrees and explains the relative explanatory depth of a generalization or relationship and its potential for control and manipulation in terms of its degree of invariance. As we will see in the next chapter, this feature of interventionism plays a central role in the interventionist account of mental causation, since it explains how mental properties can often be considered as preferable causes of

their effects in comparison to their physical realizers, given their relatively high degree of invariance.

As the discussion above should have made clear, in order for it to be true that X causes Y according to interventionism, there must exist some (at least minimally) invariant relationship between X and Y, which ensures that X causes Y, rather than being merely correlated with it. As Woodward (Ibid: 16) explains, we can therefore think of invariance as the feature, in virtue of which certain relationships and generalizations qualify as causal; a role that is usually assigned to laws of nature on other accounts of causation. What then is the relationship between laws and invariant generalizations? (Note that this issue is especially relevant to the argument in Section 4.3 below.)

It is immediately apparent that invariant generalizations do not meet one of the presumptive criteria for lawfulness, namely being exceptionless. Now, although some (Cartwright, 1980) argue that there are no truly exceptionless laws, even at the level of fundamental physics, it is usually thought that genuine laws hold without exception and that it is, at least in part, in virtue of being exceptionless that generalizations qualify as laws. For example, since the

generalization   ‘all   inertial   bodies   have   no   acceleration’   is   thought   to   be  

exceptionless and hence is thought to qualify as a genuine physical law, the status of this generalization as a law would be undermined by even one instance of an inert accelerating body (Carroll, Spring 2012).

By contrast, generalizations can qualify as invariant and genuinely causal and explanatory, even if there are some, if not many exceptions to those generalizations. This is because, as I explained above, it is only necessary for some generalization to qualify as invariant that there is some intervention on the

cause variable that changes the effect variable, allowing for the possibility that there are some (possibly many) exceptions to those generalizations.

For   example,   the   generalization   ‘Smoking   causes   cancer’   would   be  

invariant and hence qualify as causal and explanatory to the extent that the

variable   ‘cancer’   occurs   more   frequently   when   the   variable   ‘smoking’   is  

introduced via interventions than when smoking is absent.13 _{This remains true}

even though this relationship has exceptions (for example, some individuals may smoke and yet fail to develop lung cancer). Moreover, although this generalization may well be explanatorily shallow in comparison to a generalization which cites the biological mechanisms14 _{involved in the}

relationship between smoking and cancer, it is important to emphasise that both

kinds of generalizations can qualify as genuinely causal and explanatory according to interventionism, given that they both qualify as minimally invariant.

We can therefore see that whether a generalization qualifies as invariant and hence causal and explanatory is fairly independent of whether it meets one of the presumptive criteria for lawfulness, namely being exceptionless. For Woodward, this is significant because it means that interventionism is able to avoid a dilemma that other accounts of causation that appeal to a traditional account of laws inevitably face. As Woodward (2003: 239) explains, a dilemma arises because on the traditional account, it is assumed that laws (understood to be exceptionless) are required for causation and successful explanation. Then,

13 _{Citing prior research, Woodward (2003: 312) explains that since this relationship does remain} invariant across a range of circumstances, which control for confounding variables, such as gender, genetic background, variations in environment and diet and so on, it can be considered as a genuine causal generalization.

14 _{This is not to imply that mechanistic causal explanations are}

guaranteed to provide preferable explanations of some effect in  comparison  to  ‘higher-level’ (for example, sociological,

psychological) explanations of some effect, since this depends on the degree of invariance that the relationships cited in those explanation possess, and/or on which explanation captures the correct contrastive focus.

given that special science generalizations do not appear to meet this criterion, it seems that one would be forced to conclude either that special science generalizations are not laws and hence are not genuinely causal or explanatory, or that they are laws, but that they need to be qualified, hence the many complex arguments for ceteris paribus laws. Interventionists are simply able to avoid this dilemma, since according to interventionism, special science generalizations can qualify as invariant and hence causal and explanatory, even if they do not meet the traditional criteria for lawfulness. Consequently, interventionism provides a useful and convincing account of the generalizations of the special sciences and most importantly for our purposes, of the generalizations of psychology.15

Does this mean that there are no such things as laws according to interventionism? Not necessarily. As Woodward notes, there may be examples of invariant generalizations, such as the gas laws in fundamental physics that do meet the traditional criteria for lawfulness and that may rightly be called laws, or even laws of nature. However, the crucial point to emphasise is that these laws of nature are not fundamentally different in kindto  the  ‘loose  generalizations’  of  the  

special sciences; laws of nature are simply generalizations that display a very high degree of invariance, whereas the generalizations of the special sciences will typically display a lower degree of invariance. As Woodward  puts  it,  “rather  

than thinking of all invariant generalizations as laws, I urge instead that we think

of  laws  as  just  one  kind  of  invariant  generalization.”  (Ibid:  267)

15 _{Note also that if one does think that laws are required for causation and explanation, then the} generalizations of the physical sciences, especially physics, will be considered as preferable, given that it is arguably only at this level that one is likely to find generalizations that possess the standard criteria for lawfulness. By contrast, according to interventionism, there would be no automatic preference for the generalizations of the physical sciences, given that invariant generalizations can exist at any level.

One final feature of interventionism that will be useful to highlight is the distinction   between   type   and   token   causation   (or   as   Woodward   calls   it   ‘actual   causation’  or   AC).    As  should   be  clear   from   the   discussion  above,  a  type-level

causal   claim,   such   as   ‘Smoking   causes   cancer’,   implies   that   some   token-level

causal   claim,   such   as   ‘Smith’s   smoking   caused   his   cancer’,  would be true, but

does not depend for its truth on the actual obtaining of any such particular occurrence. This is because all that matters for whether this type-level claim qualifies as causal is that there exists some intervention on smoking that changes the occurrence of cancer and this may be true even if the intervention is merely hypothetical, or even if it is not practically, physically, or even nomically possible (more on this below).

By contrast, token causation does imply the truth of some type-level generalization. This is because, in order for it to be true that X is a token, or actual cause of Y according to interventionism, there must exist some (type- level) invariant relationship between the variables. It is important to be clear on two things, the relevance of which will become clear in Section 4.3 below. Firstly, this is not to say that the associated type-level generalizations will always be highly invariant and hence law-like. For example, the type-level generalization associated with the token-level   causal   claim,   ‘Smith’s   smoking   caused  his  cancer’,  (namely  ‘Smoking  causes  cancer’)  displays  a  relatively  low  

degree of invariance and, as discussed above, does not meet one of the standard criteria for lawfulness, namely being exceptionless. Secondly, this is not to say that the user of the token causal claim will always be explicitly aware of the associated type-level generalization, or that it is only in virtue of this explicit knowledge that a subject can acquire causal understanding of token-level causal

claims. This is because according to interventionism, in order for X to qualify as an actual cause of Y, there must exist some intervention that changes the actual

value of X to some other value that changes the actual value of Y to some other

value and although this implies the truth of some invariant type-level generalization between X and Y, we can consider the truth of these interventionist counterfactuals independently of any explicit knowledge of this associated type-level generalization.

Now, this is obviously not to say that our causal understanding of token- level causal claims is never explicitly accompanied or supported by knowledge of some type-level generalization. For example, the token causal claim,  ‘Smith’s   smoking   caused   his   cancer’,   may   be   accompanied   and   explained   by   the   type-

level  generalization  ‘Smoking  causes  cancer’. Rather, the point is simply that it will often not be accompanied or supported by any such explicit knowledge.16 To use Woodward’s  example,  “I  may  know  with  confidence  that  a  blow  on  the  head  

caused Jones's death, even though I do not know any relevant nontrivial deterministic generalization about the circumstances under which blows on the

head   are   followed   by   death.”   (Ibid: 75) The relevance of these points will become clear in Section 4.3 below.

16 _{This issue of causal understanding and in particular, the relationship between singular}