©The Royal Society/Richard Valencia.

Kant on experiments, hypotheses, and principles in natural philosophy

Alberto Vanzo writes…

As we have often noted on this blog, early modern experimental philosophers typically praised observations and experiments, while rejecting natural-philosophical hypotheses and assumptions not derived from experience. Along similar lines, Larry Laudan claimed that aversion to the method of hypothesis characterized “most scientists and epistemologists” from the 1720s to the end of the eighteenth century. Laudan mentioned Kant as one of the authors for whom “the method of hypothesis is fraught with difficulties”.

Immanuel Kant

Immanuel Kant

In this post, I will sketch a different reading of Kant. I will suggest that Kant, alongisde other German thinkers like von Haller, is an exception to the anti-hypothetical trend of the eighteenth century. Kant held that natural philosophers should embrace experiments and observations, but they are also allowed to formulate hypotheses and to rely on certain non-empirical assumptions. They should develop fruitful relationships between experiments and observations on the one hand, (some) hypotheses and speculations on the other.

I will illustrate Kant’s position by commenting on a sentence from the Pragmatic Anthropology: when we perform experiments,

    we must always first presuppose something here (begin with a hypothesis) from which to begin our course of investigation, and this must come about as a result of principles. (Ak. 7:223)

1. “[W]e must always first presuppose something here (begin with a hypothesis)…”

“For to venture forth blindly, trusting good luck until one stumbles over a stone and finds a piece of ore and subsequently a lode as well, is indeed bad advice for inquiry”. Even if we tried to perform experiments in a theoretical void, our activity would still be influenced by hypotheses and expectations. “Every man who makes experiments first makes hypotheses, in that he believes that this or that experiment will have these consequences” (24:889).

Like British experimental philosophers, Kant acknowledges that hypotheses and preliminary judgements may be “mere chimeras” (24:888), “romances” (24:220), castles in the air, or “empty fictions” (24:746). Hypotheses, like castles in the air, are fictions, but not all fictions must be rejected. The power of imagination, kept “under the strict oversight of reason” (A770/B798), can give rise to useful “heuristic fictions” (24:262). What is important is to be ready to reject or modify our hypotheses in the light of experimental results, so as to get closer and closer to the truth.

2. “…and this must come about as a result of principles.”

What principles are involved in our natural-philosophical investigations? As is well known, Kant holds that nature is constrained by a set of principles that we can establish a priori, like the causal law. In what follows, I will focus on three other principles that guide our experimental activity. They are the principles of homogeneity, specification, and affinity.

  • The principle of homogeneity states that “one should not multiply beginnings (principles) without necessity” (A652/B680). Kant takes it to mean that one must always search for higher genera for all the species that one knows. An example is the attempt to regard the distinction between acids and alkali “as merely a variety or varied expression of one and the same fundamental material” (A652-53/B680-81).
  • The principle of specification prohibits one from assuming that there are lowest species, that is, species which cannot in turn have sub-species. This led, for instance, to the discovery “[t]hat there are absorbent earths of different species (chalky earths and muriatic earths)” (A657/B685).
  • The principle of affinity derives from the combination of the principles of homogeneity and specification. It prompt us to look for intermediate specices between the species that we already know.

For Kant, the principles of homogeneity, specification, and affinity are not derived a posteriori from our experimental inquiries. They are a priori assumptions that guide them. We would not find higher genera, lower species, and intermediate species in the first place, unless we assumed that they exist and we tested that assumption with experiments and observations. For Kant, this is a non-empirical assumption that precedes and guides natural-philosophical inquiries. These do not unfold entirely a posteriori. They presuppose hypotheses and principles that are prior to experience and enable us to extend our knowledge of the world. Thus, rather than rejecting hypotheses and non-empirical assumptions as many experimental philosophers did, Kant holds that a guarded use of them is useful for our study of nature.

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