You can’t start a fire without a spark… and fuel… and…
Asked what a cause is, we may be tempted to say that it is an event which precedes the event of which it is the cause, and is both necessary and sufficient for the latter’s occurrence; briefly, that a cause is a necessary and sufficient preceding condition.
There are, however, many difficulties in this account. I shall try to show that what we often speak of as a cause is a condition not of this sort, but of a sort related to this. That is to say, this account needs modification, and can be modified, and when it is modified we can explain much more satisfactorily how we can arrive at much of what we ordinarily take to be causal knowledge; the claims implicit within our causal assertions can be related to the forms of the evidence on which we are often relying when we assert a causal connection.
§ 1. Singular Causal Statements
Suppose that a fire has broken out in a certain house, but has been extinguished before the house has been completely destroyed. Experts investigate the cause of the fire, and they conclude that it was caused by an electrical short-circuit at a certain place. What is the exact force of their statement that this short-circuit caused this fire?
Clearly the experts are not saying that the short-circuit was a necessary condition for this house’s catching fire at this time; they know perfectly well that a short-circuit somewhere else, or the overturning of a lighted oil stove, or any one of a number of other things might, if it had occurred, have set the house on fire. Equally, they are not saying that the short-circuit was a sufficient condition for this house’s catching fire; for if the short-circuit had occurred, but there had been no inflammable material nearby, the fire would not have broken out, and even given both the short-circuit and the inflammable material, the fire would not have occurred if, say, there had been an efficient automatic sprinkler at just the right spot.
Far from being a condition both necessary and sufficient for the fire, the short-circuit was, and is known to the experts to have been, neither necessary nor sufficient for it. In what sense, then, is it said to have caused the fire?
At least part of the answer is that there is a set of conditions (of which some are positive and some are negative), including the presence of inflammable material, the absence of a suitably placed sprinkler, and no doubt quite a number of others, which combined with the short-circuit constituted a complex condition that was sufficient for the house’s catching fire—sufficient, but not necessary, for the fire could have started in other ways. Also, of this complex condition, the short-circuit was an indispensable part: the other parts of this condition, conjoined with one another in the absence of the short-circuit, would not have produced the fire. The short-circuit which is said to have caused the fire is thus an indispensable part of a complex sufficient (but not necessary) condition of the fire.
In this case, then, the so-called cause is, and is known to be, an insufficient but necessary part of a condition which is itself unnecessary but sufficient for the result. The experts are saying, in effect, that the short-circuit is a condition of this sort, that it occurred, that the other conditions which conjoined with it form a sufficient condition were also present, and that no other sufficient condition of the house’s catching fire was present on this occasion.I suggest that when we speak of the cause of some particular event, it is often a condition of this sort that we have in mind. In view of the importance of conditions of this sort in our knowledge of and talk about causation, it will be convenient to have a short name for them: let us call such a condition (from the initial letters of the words italicized above [an insufficient; necessary part of an unnecessary, sufficient condition]), an INUS condition.
J.L. Mackie – Causes and Conditions
See also:
“Empirically sufficient and empirically necessary” – Lant Pritchett on economic growth as the (only) key to poverty reduction
Reading list – Scott Cunningham’s Causal Inference: The Mixtape
Statistical Rethinking: Richard McElreath on Bayes in the Garden of Forking Data
Quixotic Monuments to False Prediction: Oliver Kim and Morten Jervens on GDP in developing countries
Cascades, tides and shifting stars in social interventions: Megan Stevenson on cause, effect and the limits of RCTs
Natura non facit sultum*: Lant Pritchett on poverty lines
“If it was easy for them to have made a meaningful improvement, they would have done so already.”: Megan Stevenson on social change and constraints
Econtalk: Mauricio Miller on Poverty, Social Work, and the Alternative
Thought experiment: poverty and inequality without injustice
Recommendation: Rachel Glennerster on Poverty, Global Development, Randomised Controlled Trials and more
Podcast recommendation: Mark Rank and Russ Roberts on poverty in the US (Econtalk)
Will and Ariel Durant on Inequality, Redistribution, Revolution and the Nature of Society’s Wealth
Astonishing wealth inequality graphic
Russ Roberts on inequality and poverty
On inequality
Fish Forks: behavioural individuality among genetically identical fish…
Remember the name: Persistence of wealth through China’s revolutions
Harrison Bergeron: Kurt Vonnegut imagines true equality
Raj Chetty on return on investment for social programs
The haves and the have-laters