The hypothesis of Andreas Cellarius, showing the planetary motions in eccentric and epicyclical orbits.
Part of a page from John Duns Scotus's book Commentaria oxoniensia ad IV libros magistri Sententiarus, showing the words: "Pluralitas non est ponenda sine necessitate", i.e., "Plurality is not to be posited without necessity"
Manuscript illustration of William of Ockham
Possible explanations can become needlessly complex. It might be coherent, for instance, to add the involvement of leprechauns to any explanation, but Occam's razor would prevent such additions unless they were necessary.
Andreas Cellarius's illustration of the Copernican system, from the Harmonia Macrocosmica (1660). Future positions of the sun, moon and other solar system bodies can be calculated using a geocentric model (the earth is at the centre) or using a heliocentric model (the sun is at the centre). Both work, but the geocentric model arrives at the same conclusions through a much more complex system of calculations than the heliocentric model. This was pointed out in a preface to Copernicus' first edition of De revolutionibus orbium coelestium.

This philosophical razor advocates that when presented with competing hypotheses about the same prediction, one should select the solution with the fewest assumptions, and that this is not meant to be a way of choosing between hypotheses that make different predictions.

- Occam's razor

Parsimony (as in the application of "Occam's razor", discouraging the postulation of excessive numbers of entities)

- Hypothesis
The hypothesis of Andreas Cellarius, showing the planetary motions in eccentric and epicyclical orbits.

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The scientific method is often represented as an ongoing process. This diagram represents one variant, and there are many others.

Scientific method

Empirical method of acquiring knowledge that has characterized the development of science since at least the 17th century .

Empirical method of acquiring knowledge that has characterized the development of science since at least the 17th century .

The scientific method is often represented as an ongoing process. This diagram represents one variant, and there are many others.
Precession of the perihelion – exaggerated in the case of Mercury, but observed in the case of S2's apsidal precession around Sagittarius A*
Einstein's prediction (1907): Light bends in a gravitational field
Model of DNA with David Deutsch, proponent of invariant scientific explanations (2009)

It involves formulating hypotheses, via induction, based on such observations; experimental and measurement-based testing of deductions drawn from the hypotheses; and refinement (or elimination) of the hypotheses based on the experimental findings.

Occam's Razor serves as a rule of thumb for choosing the most desirable amongst a group of equally explanatory hypotheses.