To continue with the discussion, I now turn to an objection to the Humean view, given by Mackie in his 1965 paper Causes and Conditions. His objection focuses on the notion of there being an insufficient but necessary part of an unnecessary but
sufficient condition, also known as an INUS condition. In short, his objection to Hume
is to say that we need not appeal to the notion of necessary connection in order to explain causation. As such, his argument is that Hume attacks a straw man, and that as such, we have no reason to accept, for the reasons Hume gives, that we cannot explain causation as being mind-independant. In other words, if the notion of causation does not involve the notion of necessary connection, then Hume is barking up the wrong tree in attempting to explain causation, and therefore we do not need to follow him and agree that out concept is based on nothing more than that of constant conjunction. However, obviously this depends on the plausibility of Mackie’s own account, to which I now turn.
For the purpose of saving objective mind-independent cause and effect, Mackie starts his argument by posing a case in which a house is half burned down, and after a thorough investigation, the investigators announce that it was an electrical short-circuit that actually caused the fire. Regarding this case, Mackie (1965: 245) states that the short-circuit is actually neither sufficient nor necessary for the fire, and yet, it is the very cause of it. To be more particular, it is not sufficient because the short-circuit alone would not have caused the fire, there needed to be other conditions for the fire incident to happen, such as the malfunction of the sprinklers, and the flammable goods close by; also, the short-circuit is not necessary for the fire either, for something else, such as fireworks, could have caused it as well.
However, Mackie (1965: 245-246) also argues that since it is the short-circuit, the malfunction of the sprinklers, and the flammable objects close by that caused the fire, therefore, the short-circuit is part of a sufficient condition for the fire incident to happen; furthermore, the malfunction of the sprinklers and the flammable objects would not have caused the fire without the short-circuit, for this reason the short- circuit is a necessary part of this sufficient condition. Having explained this case, Mackie (1965) then goes on to conclude that the short-circuit is an insufficient but
necessary part of an unnecessary but sufficient (INUS) condition for the fire.
Furthermore, Mackie also offers his definition of this condition, which follows as:
A is an INUS condition of a result P if and only if, for some X and for some Y, (AX or Y) is a necessary and sufficient condition of P, but A is not a sufficient condition of P and X is not a sufficient condition of P. (Mackie, 1965: 246)
With regard to this definition, Mackie (1965) predicts some potential issues that might be pointed out, and accordingly adds some additional description to it. Although this account of INUS condition is an attempt to explain causation, Mackie (1965) points out that there are some causes that are non-INUS conditions. More precisely, besides INUS conditions, there are independently sufficient conditions. Take an example to explain independently sufficient conditions, say I got waken up very early this morning by a passing by truck which was particularly loud. In this case, the passing loud truck is an independently sufficient condition for my waking as the effect; furthermore, there are also causes that are necessary parts of necessary and sufficient conditions, a perfect example for this kind of causes is, according to Duxbury (2016), if one cracks eggs in boiling water, then one will end up with some
necessary and sufficient condition for the making of the poached eggs. So at this point, it seems like that there has to be an expansion on the spectrum of INUS conditions.
In response to this demand for an expansion, Mackie (1965: 247-248) states that this category of conditions does not exclusively include INUS conditions, also, it includes independently sufficient conditions as well as necessary parts of necessary and sufficient conditions. Correspondingly, Mackie (1965: 249) claims that A is a cause of P if and only if A is at least an INUS condition of P; also, A is at least an INUS condition of P if and only if (1) A is an INUS condition of P, or (2) A is an independently sufficient condition of P; or (3) A is a necessary part of a necessary and sufficient condition of P.
On the face of it, by expanding the range of INUS conditions, it successfully solves the potential problems the independently sufficient conditions and the necessary parts of necessary and sufficient conditions may cause. Yet, it is not enough to cover all the other conditions that might play a role in influencing an effect. Back to the house fire case for an example, although the short-circuit is the cause of the fire, it would not have happened without oxygen in the house, therefore, one can argue that the fact that there was oxygen in the house also played a significant role in influencing the effect which is the house being on fire, but this condition is not included in Mackie’s INUS condition category. To take this case even further, one can argue that the fact that the planet earth is not being destroyed is also a condition for the fire, so one can say that it is the fact that the planet earth is not being destroyed actually caused the fire. Due to this reason, it seems like Mackie has to either expand the INUS condition archive even further or explain the conditions like oxygen in the house fire case.
I think that it is obviously pointless to keep expanding the list of INUS condition, for there would not be an end to it, and at this point, the only solution for this problem is to find a way to explain all the other factors that also contribute to the effect of a causal relation. The solution Mackie (1965) offers is a notion called a ‘casual field’, which restricts and determines what conditions should be considered as causes and what should not. To be more specific, Mackie (1965: 249) explains this notion by first stating that the question ‘What causes influenza?’ is incomplete and indeterminate, for this question can be interpreted in two ways, one way focuses on what generally causes influenza in human bodies; the other way is to understand it as ‘given the fact that influenza is present, what it is that makes some people fall victim to it but others do not?’ Also, since these two questions concentrate on different aspects of influenza, the causal fields for these two questions are therefore different as well. According to Mackie (1965: 249), for the former way to understand it, the causal field is simply human beings, while the causal field for the latter is
human beings in conditions where influenza viruses are present. Having explained
these two ways to understand the question about influenza, it is now clear what a causal field is:
In all such cases, the cause is required to differentiate, within a wider region in which the effect sometimes occurs and sometimes does not, the sub-region in which it occurs: this wider region is the causal field. (Mackie, 1965: 249)
By setting up the restrictions of the causal field, Mackie (1965) asserts that the so called background conditions can be seen as part of the causal field, and thus a part
What is more, another important aspect of the background conditions Mackie (1965) holds is that they are fixed. For example, in the house fire case, the facts that there is oxygen in the house, and that the planet earth is not being destroyed are all
fixed background conditions, that is to say, A is a cause of P if and only if A is at least
an INUS condition of P relative to the causal field C. Following this line of reasoning, since these conditions are fixed, Mackie (1965) thinks that naturally these conditions should be seen as part of INUS conditions by default. At this point, it seems that Mackie’s strategy of the causal field successfully explains the background conditions in the context of INUS conditions, However, one issue arises here, that is, that Mackie is obliged to offer an explanation as to what actually fixes these background conditions.
There are two replies that can be made here to this enquiry, it is the context of discussion that fixes the background conditions or the causal field, or it is something else. Mackie (1965) neither says that it is the context of discussion nor does he specify anything else that could fix the background conditions. Therefore, it seems as if only the context of discussion can fix the background conditions, but then a problem occurs: if it is the context of discussion that fixes the background conditions, then it makes causation potentially subjective, which then means it is mind- dependent. Again, mind-dependence is something Mackie wants to avoid, because it will entail that causation is generated by habit, which exists only in human minds. One could reply to this by saying that the background conditions are fixed by the context in an objective way, but without any supporting evidence, this assertion itself is considered subjective. Therefore, this attempt by Mackie to preserve causation from Hume’s view does not work out. What Mackie’s (1965) theory lacks is the feature of mind-independence for the causal field, but at this point, it seems too
difficult for the advocate of mind-independant causation to obtain such independence and to also offer a convincing account over it. And so I conclude that Hume’s argument survives Mackie’s attempt to offer an alternative account.