As mentioned in my previous essay, Isis (my Siberian husky) fell victim to the ravages of time. Once a sprinting blur of fur, she was reduced to sauntering. Still, lesser beasts feared her (and to a husky, all creatures are lesser beasts) and the sun was warm in the backyard, so her life was good even at the end.  

Faced with the challenge of keeping her healthy and happy, I relied a great deal on what I learned as a philosopher. As noted in the preceding essay, my philosophical skills kept me from falling victim to the post hoc fallacy and the fallacy of anecdotal evidence. In this essay I will focus on two basic, but extremely useful methods of causal reasoning.

One of the most useful tools for causal reasoning is the method of difference. This method was famously developed by the philosopher John Stuart Mill and has been a staple in critical thinking classes since before my time. The purpose of the method is figuring out the cause of an effect, such as a husky suffering from a knuckling paw (a paw that folds over, so the dog is walking on the top of the foot rather than the bottom). The method can also be used to try to sort out the effect of a suspected cause, such as the efficacy of an herbal supplement in treating canine arthritis.

Fortunately, the method is simple. To use it, you need at least two cases: one in which the effect has occurred and one in which it has not. In terms of working out the cause, more cases are better, although more cases of something bad (like arthritis pain) would be undesirable from other standpoints. The two cases can involve the same individual at different times as it need not be different individuals (though it also works in those cases as well). For example, when sorting out Isis’ knuckling problem the case in which the effect occurred was when Isis was suffering from knuckling and the case in which it did not was when Isis was not suffering from this problem. I also investigated other cases in which dogs suffered from knuckling issues and when they did not.

The cases in which the effect is present and those in which it is absent are then compared to determine the difference between the cases. The goal is to sort out which factor or factors made the difference. When doing this, it is important to keep in mind that it is easy to fall victim to the post hoc fallacy and conclude without adequate evidence that a difference is a cause because the effect occurred after that difference. Avoiding this mistake requires considering that the “connection” between the suspected cause and the effect might be a coincidence. For example, Isis ate some peanut butter the day she started knuckling, but it is unlikely that had any effect, especially since she ate peanut butter since we became a pack. It is also important to consider that an alleged cause might be an effect caused by a factor that is also producing the effect one is concerned about. For example, a person might think that a dog’s limping is causing knuckling, but they might both be effects of a third factor, such as arthritis or nerve damage.

You must also keep in mind the possibility of reversed causation, which is when the alleged cause is the effect. For example, a person might think that limping is causing knuckling, but it might turn out that the knuckling is the cause of the limping.

In some cases, sorting out the cause can be easy. For example, if a dog slips and falls, then has trouble walking, the most likely cause is the fall. But it could still be something else. In other cases, sorting out the cause can be difficult. It might be because there are many possible causal factors. For example, knuckling can be caused by many things (even Lyme disease). It might also be because there are no clear differences (such as when a dog starts limping with no clear preceding event). One useful approach is to do research using reliable sources. Another, which is a good idea with pet problems, is to refer to an expert, such as a vet. Medical tests, for example, are useful for sorting out the differences and finding a likely cause.

The same basic method can also be used in reverse, such as determining the effectiveness of a dietary supplement for treating canine arthritis. For example, when Isis started slowing down and showing signs of soreness, I started giving her senior dog food, glucosamine and extra protein. What followed was an improvement in her mobility and the absence of soreness. While the change might have been a mere coincidence, it is reasonable to consider that one or more of these factors helped her. After all, there is some scientific evidence that diet can have an influence on these things. From a practical standpoint, I decided to keep to this plan since the cost of the extras is low, they have no harmful side effects, and there is some indication that they work. I did consider that I could be wrong. Fortunately, I did have good evidence that the steroids Isis was prescribed worked as she made a remarkable improvement after starting them and there is solid scientific evidence that they are effective at treating pain and inflammation. As such, it is rational to accept that the steroids were the cause of her improvement, though this could also be a coincidence.

The second method is the method of agreement. Like difference, this requires at least two cases. Unlike difference, the effect is present in all cases. In this method, the cases exhibiting the effect (such as knuckling) are considered to find a common thread in all the cases. For example, each incident of knuckling would be examined to determine what they all have in common. The common factor (or factors) that is the most plausible cause of the effect is what should be taken as the likely cause. As with the method of difference, it is important to consider such factors as coincidence to avoid falling into a post hoc fallacy.

The method of agreement is most often used to form a hypothesis about a likely cause. The next step is, if possible, to apply the method of difference by comparing similar cases in which the effect did not occur. Roughly put, the approach would be to ask what all the cases have in common, then determine if that common factor is absent in cases in which the effect is also absent. For example, a person investigating knuckling might begin by considering what all the knuckling cases have in common and then see if that common factor is absent in cases in which knuckling did not occur.

One of the main weaknesses of these methods is that they tend to have very small sample sizes, sometimes just one individual, such as my husky. While these methods are quite useful, they can be supplemented by general causal reasoning in the form of experiments and studies, which is the subject of the next essay in this series.