Science isn’t so complicated once you understand the main concepts. Once you understand them you can’t be so easily fooled by media or school. These main concepts exist in all the sciences, and understanding these concepts will help you think critically about any science.

Philosophers of science specialize in discerning what these key words mean. There is not always agreement among them, but there is a general pattern of agreement, which is based on both learning about different sciences as well as thinking critically about why specific words are used by scientists rather than others. You, too, can understand science by examining these commonly used words:

Hypothesis     Evidence     Fact     Law     Theory     “Natural”



Since Indian classical music can affect bacterial growth rates, then perhaps different types of music affect bacterial growth rate differently.

If the genetic code contains a language, then it should match the definition of language developed by linguists.

A hypothesis is a since/then or if/then statement. “Since” refers to previous research, “if” refers to a guess, possibility, or speculation, and “then” refers to the result a scientist expects after doing the research. Thus, a hypothesis is an expectation that one thing will lead to or be related to another.

A hypothesis must be worded in a way that makes it possible to confidently determine whether the result was (almost) as expected, and also whether it was not (anywhere close) as expected. Scientists use mathematics to translate their confidence into a statistic, called “statistical significance”. The greater the statistical significance, the greater their confidence. If the result is not as expected, then a scientist might change the wording of the original hypothesis so that it matches the result. Astrophysicist John Bahcall did this before submitting the results of his Homestake experiment for publication [Schuster, ch. 9, p. 145].

Hypothesis originates from the Greek hypo (less than) and thesis (proposition). A hypothesis is less than a proposition because it does not propose something as true, but only possibly true.

Is a Hypothesis Necessary?

Sometimes scientists claim that a prediction must be made in order to do science; researchers must expect a result. This claim is based on the belief that “real” science must be capable of being proved wrong. Thus, doing research to satisfy curiosity is sometimes not considered to be actual science.

These scientists are wrong, however. Many journals publish scientific papers that do not test a hypothesis, such as this paper about the effect on the elderly of consuming whey protein. The authors do not have expectations. But, thanks to their curiosity, other scientists can develop hypotheses based on their research.


In science, evidence is the “then” part of a hypothesis that–after the hypothesis is worded–is sensed, experienced, perceived through the external senses of sight, hearing, smell, taste, or touch. It can be perceived directly through our biological instruments (ie. eyes, ears, nose, tongue, or fingers), or inferred through mathematics and artificial instruments. Sometimes whatever is perceived is essentially a pattern that has been given a name. For example, “intelligence” cannot be detected with the external senses, but behaviors can, and a pattern of behaviors can be named “intelligence”.

Because there are different ways of testing the same hypothesis, scientists can have different experiences, and hence different evidence, resulting from those tests. For example, a group of six scientists found support for a hypothesis concerning sexual bias in biology, and three groups comprising seven scientists total did not find support when using different methods [sources].

Emotion, intuition, imagination, and critical thought are also sensed, experienced, and perceived, but these are not scientific evidence because these are not usually experienced consistently. Even when thinking critically scientists do not always have the same opinions. Due to the different ways to test a hypothesis, scientists might believe one study used good methods and another study used bad methods. Not only do they sometimes disagree about which methods were good and which were bad, but sometimes the results will bias their interpretation the quality. Although critical thought does not guarantee agreement, it is still necessary when evaluating and designing methods of gathering evidence.

There is evidence that is not scientific evidence, such as testimonial evidence.


In science, a fact is 1) a supported hypothesis 2) in a paper that has been reviewed by colleagues and 3) published in a scientific journal. Sometimes different scientists test the same hypothesis, but some tests result in support for it while others do not. This means the evidence differs among those papers, which means the facts differ. For example, doctors in the past recommended low-fat diets for weight loss because the facts supported such a recommendation, but today there are more facts that low carbohydrate diets are superior to low fat diets for weight loss. Facts are not always consistent.

If scientists begin to have experiences that are consistently different from the evidence acquired previously, then they will consistently record this in their papers, and a new fact replaces the old. However, sometimes the name they give to the fact remains the same. For example, today’s chemists describe their experience of oxygen in a manner significantly different compared to the description made by Antoine Lavoisier. Thus, the fact concerning “oxygen” changed, but the name “oxygen” did not, making it appear as though the fact did not change [Schuster, Ch. 4).

Since facts can change, then a fact is not necessarily true. For example, a 2012 study concluded that conservatives were more likely to have traits associated with psychoticism compared to liberals, but in 2016 the researchers issued a correction stating that the data actually showed the opposite. For four years the published result was a fact. After the correction, the opposite was a fact.

In science, the “truth” can change.

There are facts that are not scientific facts, such as journalistic facts.


Related to fact is interpretation. These are inferences, meanings, and “takeaways” scientists express in their papers. Interpretations are based on facts, but they are not facts because their “truth” cannot be perceived with one of the five senses. An interpretation gives a fact value. It gives a scientist a reason to care about it. Sometimes scientists have different interpretations of the same facts.


In science, there are three meanings of “law”. One is that it is a description about a pattern of behavior that is always or practically always perceived. For example, all information-coding molecules… Language such as “That is inconsistent with the law of x” expresses the belief that a law is only a description about what is normally perceived. Following this belief, behavior that is radically out-of-the-ordinary is improbable, but not impossible.

A second meaning is that a law is an entity that causes what we (practically) always experience or prevents what we (practically) never experience. Language such as “This and that happens because of the Law of Such-and-Such” reflects the belief that a law causes an event. Language such as “That violates the Law of Such-and-Such” reflects the belief that a law prevents an event. Anything that “breaks a law” is impossible, because–fundamentally–all events are ruled by laws.

A third meaning unifies the other two. It relies on the recognition that things are bestowed with characteristics, properties, attributes that are capable of acting as causes. Events are caused by the properties of a thing that have the ability to be causes. A scientific law is a description of the pattern of events that these attributes repeatedly cause.

The more diverse a pattern of behavior is, the less likely a law can describe it. A law is pronounced by scientists only after multiple, multiple, multiple occasions of perceiving the same pattern of behavior.


“That’s just a theory.”

Scientists hate that. That statement trivializes the idea of a theory, and scientists really be lovin’ their theories. But, sometimes scientists cause confusion about the meaning of ‘theory’ when they say, “in theory…” or “theoretically” rather than “hypothetically”, as they should. 

Whereas a law describes what, a theory describes how or why. It originates from the Latin theo, and means literally “of God”, “to God”, or more contextually “to see God”.

Theory is Perspective

There are many scientific fields. Different scientists study different things, which means they describe how things behave differently. But, generally, a theory is a framework, lens, perspective used to interpret patterns of behavior, and used to make more hypotheses. More hypotheses leads to more facts. Theories help scientists to take a bunch of evidence that really, really seems related, and organize it. Then, to connect the dots so that they can see the bigger picture–more related facts.

One the one hand, theories enable scientists to focus on particular characteristics, properties, attributes of evidence, and have a more focused perspective. On the other hand, habitually focusing with one perspective can make it difficult to see from another perspective. Other theories may be rejected because accepting them requires breaking a habit, and habits are hard to break.

Theory is Language

Theories provide a vocabulary or language with which to talk about a particular subject, and must be worded such that evidence could be either consistent or inconsistent with the description of ‘how’. They can be slightly revised to describe inconsistent expectations. However, theories should not be revised to describe opposite expectations. If a theory were revised to describe opposite expectations, then no evidence could be inconsistent with the theory. This would make it not a theory, but a scientific field.

The language that theories provide for communication is related to the perspective they offer for interpretation: language and perspective shape one another. Since changing a habitual perspective is challenging, and since perspective and language shape one another, then changing the language use to describe how can be challenging. Thus, scientists can experience difficulty replacing one theory with its superior, and can prefer to continually revise the inferior theory using already existing language. But, the more revisions needed, the more likely a theory would need to be rejected. 

Rejected Theories

Theories that are rejected still maintain the status of ‘theory’. Therefore, a theory is not necessarily supported by evidence. Obsolete theories (eg. theory of circular inertia) are still theories just as disconfirmed hypotheses are still hypotheses and bad science is still science [Laudan].

Given that a theory can be obsolete while maintaining its status as a theory, then a theory cannot be a fact. If a “fact” is obsolete, then it is not a fact. A theory can be slightly modified and still be the same theory, but a fact cannot be modified. A “modified fact” is a different fact.

Natural, Material, and Physical

Practically every scientist and philosopher of science will say that scientists can study only things that are natural, material, or physical. However, there is no scientific definition of these words. There is currently no method to determine if a thing being studied has these attributes. Given that use of such a method would require scientists to first study the thing prior to determining if it has these attributes, then obviously a thing can be studied without knowing whether it is natural, material, or physical. Thus, for the purpose of doing science, these are not a relevant concepts.

Because they are not relevant to conducting scientific research, then “pseudophysical”, “quasimaterial”, “supernatural”, mega-, hyper, hypo-, sub-, hemi-, anti-, contra-, or any other prefix/noun combination is likewise not relevant. What matters is whether something can be perceived with at least one of the external senses and critically examined, or inferred from something that can be perceived with one of the external senses and critically examined (eg. dark matter).


Laudan, Larry. Science and Values: the aims of science and their role in scientific debate. University of California Press, 1984. P. 121

Schuster, John. An Introduction to the History and Social Studies of Science. 1995. PDF

Sex Bias
Budden,A.E., Tregenza,T., Aarssen, L.W., Koricheva, J., Leimu, R.& Lortie, C. J. (2008). Double-blind review favours increased representation of female authors. Trends in Ecology & Evolution, 23, 4-6.

Engqvist, Leif; Frommen, Joachim G. (2008). Double-blind peer review and gender publication bias. Animal Behaviour, 76 (3), e1-e2.

Webb, T. J., O’Hara, B., & Freckleton, R. P. (2008). Does double-blind review benefit female authors? Trends in Ecology & Evolution,  23 (7), 351-353.

Whittaker, R.J., 2008. Journal review and gender equality: a critical comment on Budden et al. Trends in Ecology and Evolution 23, 478–479.


Achinstein, Peter. Scientific Evidence: philosophical theories and applications. The John Hopkins University Press, 2005.

Barnard, Chris, Francis Gilbert and Peter McGregor. Asking Questions in Biology: a guide to hypothesis-testing, experimental design and presentation in practical work and research projects 3rd ed. Pearson Education Limited, 2007.

Darian, Steve. Understanding the Language of Science. University of Texas Press, 2003.

Derry, Gregory. What Science Is and How it Works. Princeton University Press, 1999.

Dewitt, Richard. Worldviews: an introduction to the history and philosophy of science. Blackwell, 2004.

Faye, Jan. Rethinking Science: a philosophical introduction to the unity of science. Ashgate Publishing Company, 2002.

Godfrey-Smith, Peter. Theory and Reality: an introduction to the philosophy of science. University of Chicago Press, 2003.

Kasser, Jeffrey, L. Philosophy of Science. The Teaching Company, 2006. DVD.

MacHammer, Peter and Michael Silberstein (eds). The Blackwell Guide to the Philosophy of Science. Wiley-Blackwell, 2002.

Pigliucci, Massimo. Nonsense On Stilts. University of Chicago Press, 2010.

Sankey, Howard, ed. Causation and Laws of Nature. Kluwer Academic Publishers, 1999. p. 11