The principle behind Occam's razor was not formulated by William of Occam, but by philosophers such as Aristotle, Maimonides, etc. Despite this, it is associated with him due to his frequent and efficient use of the principle in various endeavors during the course of his life.

The term "Occam's razor" was first mentioned in the writings of Sir William Hamilton. It was named after William of Ockham, an English Franciscan friar, theologian, philosopher, and nominalist. It is not a reference to an actual razor but rather implies that when one is faced with a situation where two hypotheses must be differentiated between, one must "shave" away unnecessary assumptions or "cut" between the two similar conclusions. It is often quoted in one of its original Latin forms to lend authenticity to it, and they are;

• Entia non sunt multiplicanda praeter necessitatem.- Entities must not be multiplied beyond necessity.
• Pluralitas non est ponenda sine neccesitate.- Plurality should not be posited without necessity.
• Frustra fit per plura quod potest fieri per pauciora.- It is futile to do with more things that which can be done with fewer.

The principle implies that when faced with competing hypotheses, the one with the fewer assumptions and conditions should be selected over the other. It does, however, allow for the fact that the more complicated solutions may or may not prove correct in light of new evidence, but till such evidence is found, it is better to make as few assumptions as possible. However, this principle must be applied in the same context to both arguments, in order to get an appropriate result. To ensure the correct use of this principle a few guidelines must be followed, they are as follows:

• Both hypotheses must possess similar predictive power with regards to the end result.
• Ad hoc reasoning should not be used to explain and add new data.
• Both theories must be scientific (falsifiable).
• All assumptions being made should be made clear and sufficiently elucidated.
• Any variables described, must be well-defined.

These conditions can be explained as follows. Lets consider two hypotheses - First, the computer works on electricity, and second, the computer works because of aliens or magic. Both these theories have the same predictive power,i.e., the computer works, and they also exhibit a slight degree of falsifiability in case the computer stops working. Next, if we define the terms of the hypotheses, the first theory would be - the computer possesses a circuit system, power is drawn by this system from the mains, the conductance of power through the circuit allows the computer to function. The term of the second theory would be - computer possesses a circuit system, power is drawn by it from the mains, but power passing through the circuit does not cause the computer to work, it works due to an invisible and undetectable force applied by foreign elements, and this requires no extra components to be fitted to the computer. Here it is clear which theory has the least amount of terms or conditions. For defining variables, if we consider an equation such as (2X + 3 = 7) where no variables are defined, the simplest explanation is to solve for X and assume that X=2. The undefined vague theory would lead to the inference of X=D, where even d is not defined and is merely a renamed X. Creationists and conspiracy theorists often use the principle of Occam's razor incorrectly as a tool to put forth their theories as being right. They refuse credible experimental evidence in favor of a completely unknown entity that functions via a mysterious and equally unknown mechanism. The common example is that of creationism vs. evolution. Despite the overwhelming evidence present in support of natural selection and evolution, the creationists argue that it is a highly complicated mechanism. The easier mechanism, that God created the world in 7 days, must be the accurate mechanism. They use Occam's razor as the evidence itself instead of finding actual evidence to refute the competing theory of evolution. ★ Albert Einstein and Hendrik Antoon Lorentz, both made the simultaneous mathematical conclusion that passage of time is affected when an object's speed is increased. However, they both had different explanations for this change in the space-time continuum. Einstein proposed his theory of relativity, whereas Lorentz proposed that these changes were due to changes in the "ether", a substance that does not exist according to science. Therefore, by the use of Occam's razor and other supporting evidence, Einstein's theory of relativity won over Lorentz's theory of "ether". ★ It is used as a heuristic tool during the development of a model of a particular reaction mechanism, in chemistry. ★ It is used to determine the ancient migration patterns of species and populations by observing geographical features and the inter-species relationships. Migrations paths are inferred from those patterns that would require the least amount of movement of the entire population or species. ★ It is used to rule out possibilities of medical conditions when diagnosing a patients injury, ailment, illness, or disorder. In cases, where a plethora of symptoms exist or there is presence of clashing symptoms, the simpler and logical explanation is that the individual has more than one disease, instead on a singular rare disease. ★ It can also be used to differentiate between situations that have a valid cause from situations that are illusory correlations in nature. ★ It can also be used to exhibit the baseless nature of superstitions. ★ In the event that you hear creaking noises in a house where you live alone, it is more likely that it is due to the rusty hinges of the door, rather than due to the presence of a paranormal being. ★ If your bag's strap suddenly breaks, the simpler solution is that the strap was under strain and broke apart due to erosion, rather than the alternative that someone cut your bag strap. ★ You feel nauseous after eating something. It is more likely that you are experiencing food poisoning, rather than the possibility that you have stomach cancer. ★ If a person is seen scratching an area of skin, it may just be a temporary itch rather than a case of ringworm.