©The Royal Society/Richard Valencia.

Feijoo and his ‘Magisterio de la experiencia’ (lessons of experience), Part III

Juan Gomez writes…

In my last two posts I commented on an essay by Benito Feijoo. First we examined how he pictures the history of philosophy as the contest between two ladies —Solidína (experience) and Idearia (imagination) — to conquer the world. He sides with experience, and we also examined some of the arguments he gives to support the adoption of the experimental method and the rejection of mere speculation. In today’s post I want to follow Feijoo further, examining in particular his thought that just as we must abandon speculation when it is unaided by experience, we must also be cautious and keep in mind that experience without reasoning can also lead us astray in our quest for knowledge.

After spending most of his essay showing (through examples) that the proper path to knowledge is to follow the experimental method, Feijoo concludes with 3 capital errors that frequently take place in our experimental observations:

    We shall conclude this discourse, by pointing out three capital errors, which stem from lack of reflection in experimental observations. The first is that of taking for the effect that which is cause, and for cause that which is effect. The second is to take for cause something that only happens accidentally and has no influence at all. The third is, between two effects of the same cause, to take one as the cause of the other. I shall show examples of these three errors in observations pertaining to Medicine.

Of the first type of mistake Feijoo gives us a case where someone drinks water excessively to quench an overwhelming thirst. A few hours later such person suffers a fever, and it is commonly thought that the cause of the fever is the excessive consumption of water. However this is a false conclusion due to the lack of reflection when observing. If we reason, we can see that the sickness is the cause of the thirst that leads to the excessive consumption of water.

Feijoo warns us that this kind of mistake is very dangerous in medicine, since the lack of reflection and reasoning leads the physician to err in his diagnosis and prevent him from curing the disease.

The second kind of mistake takes place when we assign as the cause something that only happens accidentally. Feijoo tells us that this mistake is committed frequently by ‘superstitious souls’ that constantly assign to their diseases causes that have nothing to do with it. The most common mistaken cause in these cases is the weather. Patients frequently blame their disease on the weather: If during summer the weather is hot, the disease is taken to be caused by the excessive heat, but if summer is not hot enough, then this is also taken to be the cause of the disease.

Finally, the third kind of mistake happens when between two effects of the same cause we take one to be the cause of the other. Feijoo’s example is that of a man that performs an intense physical exercise or activity, then drinks alcohol in excess, and later suffers a fever. While most men would take the excessive drinking to be the cause of the fever, the truth is that intense exercise is more likely to cause a fever than excessive drinking.

This account of capital errors in experimental observation concludes Feijoo’s essay. So what are we to make of his thoughts on the ‘Lessons of Experience’? Well I believe that in Feijoo we have a clear example of the dispersion of the experimental method across the Iberian Peninsula in the first half of the eighteenth century. Feijoo might be the most influential figure of this period in Spain, but he certainly was not alone in the adoption and promotion of the experimental method: Andres Piquer, Manuel Martinez, Juan de Cabriada, and the circles of doctors in Seville and Valencia all shared the beliefs Feijoo expresses in his text. As we have seen in Feijoo’s work, the novatores believed that the correct path towards knowledge was the one taken by Bacon, Boyle, and Newton.

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