Occam's razor - also called the principle of parsimony - is a heuristic research principle from scholasticism, which enjoins the highest possible parsimony in the formation of explanatory hypotheses and theories.

Named after William of Ockham (1288-1347), the principle finds its application in the philosophy of science and scientific methodology. Put simply, it states:

1. of several sufficient possible explanations for one and the same state of affairs, the simplest theory is preferable to all others.

2. a theory is simple if it contains as few variables and hypotheses as possible and if these variables and hypotheses are related to each other in clear logical relationships from which the facts to be explained follow logically.

This maxim does not contradict the conclusion that multiple causes can occur in a system. The metaphorical designation as a razor results from the fact that all other explanations of a phenomenon can be removed easily and at once, as with a razor.

The practical advantage of this principle for theory discovery is that theories with few and simple assumptions are more easily falsifiable than those with many and complicated assumptions. Ockham's razor, however, is only one of several criteria for the quality of theories. It cannot be used to judge the validity of explanatory models, but it can be used to weed out unnecessary assumptions.
Walter Chatton, a contemporary of William of Ockham, took a counterposition to Ockham's parsimony principle: "If three things are not enough to make a clear statement about something, a fourth must be added, and so on." Although various other philosophers formulated similar "counter-principles" during this period, this did not change the meaning of the ontological principle of parsimony.


Origin of the term

The most famous formulation of Ockham's principle comes from the philosopher Johannes Clauberg (1622-1665). He wrote in 1654, "Entities must not be multiplied beyond what is necessary." In the form "non sunt multiplicanda entia sine necessitate," the phrase is found as early as 1639 in the Scotist Johannes Poncius, who cites it as a scholastic maxim.

The term Occam's Razor for this principle of parsimony first appeared in the 19th century in the work of the British philosopher Sir William Hamilton and gained currency in the discussion led by John Stuart Mill on his philosophy of science. William of Ockham never formulated the principle explicitly, but he applied it implicitly in his writings. For example, he urged, "Nothing may be assumed without its own justification, unless it be evident, or known by experience, or secured by the authority of Scripture."

In addition to Occam's Razor, the phrase law of parsimony is also common in English. The Latin term is novacula Occami, the traditional German Ockham's Scalpel. In French, the phrase rasoir des nominaux is found in 1746 by Étienne Bonnot de Condillac.


The principle from today's point of view

In modern philosophy of science there are various reinterpretations of "Ockham's razor", which are supposed to justify this principle as a rational research maxim. Among other things, simplicity has been associated with a higher degree of confirmation or with the best explanation. Also a higher a priori probability within the Bayesian concept of probability justifies the preference of simpler theories.

Moreover, the more independent assumptions are assumed to be a prerequisite for the explanation, the higher is the probability that one of them could be wrong. Against such justifications it is objected that they become circular if they do not have an independent criterion for the simplicity of theories. Moreover, it is argued that because of the problem of induction, it is not possible to single out as true or more probable one of several theories that are equally consistent with all given facts, regardless of how complex it is.

Contemporary rationales that seek to avoid circularity and the induction problem therefore interpret Ockham's principle as an efficient "search strategy" or heuristic: by repeatedly applying the principle to select among different explanations compatible with the data, the goal is to converge on a true general theory.


What the principle does not mean

Nevertheless, the principle is far from uncontroversial, although this may also be due to the fact that there is a vulgar understanding of the term. This would be formulated as "simple explanations are generally better than complex explanations." This, of course, invites misuse and, in the metaphor of the razor itself, shows that one can cut oneself on this sharp blade. Unfortunately, this understanding, itself greatly reduced and thus misrepresented in its meaningfulness, is repeatedly reproduced incorrectly, especially in pop-cultural contexts such as memes and comics.

With this false understanding - and not based on the formation of explanatory hypotheses and theories according to the principle of parsimony - the door would be open for the psychological mechanics of conspiracy theories. The human brain is lazy in the sense that it usually wants to save energy. As simple as possible explanations for complex facts can therefore be preferred impulsively. Of course, this is in stark contrast to science itself, which lives on efforts, setbacks and many small successes strung together.

The common sense, also to be called a sane understanding, may be another form of knowledge, which became a general fact by reduction. Proverbs and certain aphorisms are reproduced again and again until they can penetrate into the collective subconscious of the people. Here, too, the wrong understanding of Occam's razor is at the basis, because it is obvious that a boiling down of complex facts to a general understanding must necessarily lead to losses in the determination of truth. The abstract understanding of common sense itself, therefore, is to be contrasted with the equally abstract understanding of an expert knowledge: the latter knows how to use the razor in a methodically correct way, even if he often lacks the didactic ability to make the complex results of his research accessible to the layman in turn.

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