Ignaz semmelweis

27th November 2020

He worked in the first maternal division of the Vienna General Hospital. He conducted observations on a mysterious disease, the puerperal fever:
pregnant women died of such disease more in a division than in another division; both the source of the disease and the reason why one division was more affected than the other were unknown.

Hempel was quite fascinated about Semmelweis observations, considering it the perfect example of the H-D reasoning.
The problem is not approached by reasoning inductively: Semmelweis outlined several different hypotheses, testing them with evidence or by slightly modifying them.

This until he stumbled upon an event which seemed to be a more promising one: a colleague was wounded by an assistant with the same scalpel used to perform an autopsy; he contracted symptoms similar to the ones in the mothers, and eventually died.
He then supposes that the transmission of the infection were caused by doctors not cleaning their hands after coming out of the morgue.
The doctors were suggested to wash their hands, and the mortality decreased.

Before, modus tollens: a high risk of falling into a fallacy: therefore, he tests his predictions by means of other hypotheses. This was not very well received by the medical community.

The difference from Popper pseudo-science lies in confutating and testing the evidence in support of an hypothesis, not dogmatically building other rules to support the most promising one.

where to use induction:

even extensive testing with entirely favourable results does not establish a hypothesis conclusively, but provides only more or less strong support for it. Hence, […] it [scientific inquiry] may be said to be inductive in a wider sense, inasmuch as it involves the acceptance of hypotheses on the basis of data that afford no deductively conclusive evidence, but lend it more or less strong ‘inductive support’ or confirmation.

Hempel, Phil Nat Sci, p.18

Predictions are used to test the hypotheses

Logical problems of H-D in this context

First problem

  • H: if doctors wash their hands with chlorine morality falls
  • A: further premise: chlorine destroys infectious matter, unlike soap

If H and A, then p

if not p, we can’t understand if the falsity lies in A or H

Second problem

Semmelweis starting point was to be discovered, supposed, not given.

  • How do we find an hypotheses able to account for the situation?
  • How do we find a good hypotheses?

What type of explanation are we providing?

not why x, but why x instead of y

Comparison among hypotheses.

Semmelweis is not simply assessing each hypotheses singularly, but he embarks in a very research program, trying to understand what works and what not. It’s not a mere “happy guess”, but Semmelweis acts in a very preparatory ground.



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