Explain the Difference Between Theory, Law, and a Fact

Within scientific communities, “theory,” “law,” and “fact” are technical terms which have distinct and complex meanings. Many people who do not have a scientific background—including students in introductory science classes in high school and colleges—do not have a firm understanding of the differences between these three terms. Many adults are also unaware of the distinctions between these three terms, and can benefit from a polite, conversational explanation. This article will help you understand and explain the differences between proper scientific uses for each of the three terms.

Steps

Explaining the Difference between Scientific Theory and Law

1. Define a scientific law. Understanding law is fundamental to understanding scientific terminology: a scientific law is a statement, based on repeated long-term observation, which describes any phenomena of nature.
   • Laws have never been refuted (hence their relatively small number) and are not explanations; they are descriptions and are often stated through relatively simple mathematical equations.
   • Scientific laws, despite their formality, can change or have exceptions as scientific understandings of phenomena evolve.
2. Provide examples of laws. Helping someone understand scientific law—an admittedly abstract concept—will allow them to differentiate between theory and fact. In many ways, laws are a starting place; they are often observed and have never been refuted, but do not explain why something occurs.
   • A common example is the Law of Evolution: this law describes a phenomenon that has been observed throughout nature, but the law does not explain why evolution occurs.
   • As another example, the Law of Gravity has been known in the scientific community since the late 17th century. The law describes the natural phenomenon of gravity, but does not provide an explanation as to how and why gravity functions.
3. Define a scientific theory. Scientifically speaking, a theory is a rational explanation of why an aspect of our world functions in a certain way. The definition of a theory will incorporate facts and laws, although the three are fundamentally separate.
   • A theory builds from initial hypotheses (educated guesses) and can be revised in accordance with the development of a scientific understanding of a phenomena’s cause.
   • A theory is confirmed by all available evidence such that it can be used to predict new, as yet unobserved phenomena.
4. Provide an example of scientific theory. This will help clarify your point and make a clearer explanation. The theory is used to explain an occurrence, while the law describes a phenomenon under specific circumstances in nature.
   • For example, the scientific Theory of Natural Selection corresponds with the Law of Evolution. While the law states an observed natural phenomena (life forms develop new characteristics based on external circumstances), the theory describes how and why this happens.

Explaining the Difference between Scientific Law and Fact

1. Define a scientific fact. In scientific terminology, a fact is an observation that has been repeatedly observed and is accepted as practically functional and “correct.”
   • While facts can be scientifically refuted or may not be consistent across time and place, they are held as true until they have been proven wrong.
2. Provide examples of scientific facts. As you explain this concept, focus especially from separating fact from law, since both describe natural phenomena, albeit in different ways.
   • When explaining a scientific fact, start with a point of general observation.
   • For example, begin your explanation by saying something like, “it is always bright outside at noon.” This is a fact in that it describes a state of nature—however, this statement may not be true in Antarctica or Greenland, where darkness lasts throughout the day in certain seasons.
   • Explain how this will lead to a revision of the scientific fact: “within certain degrees of latitude, it is always bright outside at noon.”
3. Clarify the distinction between scientific laws and facts. Facts are often the initial building blocks of scientific inquiry; they can generate curiosity and the hypotheses that come from inquiry and experimentation.
   • Facts are less formal than laws, and are not seen as an “official” definition of a phenomenon that occurs or of the reason that something happens.
   • Facts are more localized and generalize less than laws. Explain that, if the Law of Evolution describes the way that species throughout the world evolve over time, a scientific fact related to evolution (and natural selection) could be: “giraffes with long necks can reach more leaves than giraffes with short necks.”
4. Clear up any common misconceptions. Many students and adults hold to misunderstandings of scientific vocabulary and misunderstand the relationship of theories, laws, and facts.
   • For example, scientific theories do not develop into scientific laws. To explain the difference, focus on this distinction: laws describe phenomena, while theories explain phenomena.

Explaining Scientific Theories, Laws, and Facts in the Classroom

1. Ask your students to define some scientific theories. You can build from their own understandings to develop a more sophisticated definition of “theory.” A good definition should clarify that a scientific theory is a statement intending to explain natural phenomena. Clarify to your students:
   • A theory is worth very little if it doesn't correctly predict all known evidence.
   • Theories are subject to changes as new evidence becomes available. (Most theories that you will discuss in a high school science class are well-confirmed and are unlikely to be revised in any significant sense.)
2. Ask the students to name some scientific theories. You will get some common answers like:
   • The theory of relativity: that the laws of physics are the same for all observers
   • The theory of evolution by natural selection: that the observed changes in species occur due to selection of well adapted specimens over less well adapted specimens.
   • Big Bang theory: that the universe began as an infinitely small point that underwent expansion to form the universe as we know it today.
3. Define a scientific fact for your students. A fact is an objective, verifiable observation, which is the same everywhere. It can be, and has been, verified many times.
   • For example, we know that the germ theory of illness is a fact because we can take bacteria from someone suffering from an illness, look at that bacteria under a microscope, and then inject that bacteria into another individual, who will then get that same illness.
   • We know that the Earth is round because we can travel due west and eventually end up where we started from.
4. Clarify that theories can never be transformed into a fact; the two are fundamentally different. Remember, a theory is a general statement intended to explain facts. As a useful example, present your students with the development of the theory of the heliocentric theory and the facts that inform the theory.
   • Ancient peoples noticed peculiar points of light that “wandered” among their background. (We now know these to be the planets.)
   • The planets moved through the sky because they, like the Earth, were orbiting around the sun, each at different speeds, different distances from the Sun.
   • Nicolaus Copernicus is generally considered to be the first to propose this theory, and supported his theory with hard evidence, but ancient cultures stumbled upon this through speculation.
   • We now consider this a fact because we have sent many craft to these planets and can predict their motions to a very high precision. Of course, our predictions come from the theory (and the laws underlying that theory).
5. Define a scientific law. This is a complicated concept and tends to confuse students. Laws tend to be more mathematical in nature and are usually derived from simple statements about mathematical systems and their behaviors. Explain that, like a theory, a law can also be used to make predictions, but the primary purpose of a law is to describe natural phenomena. Some scientific laws include:
   • Newton's Law of heating and cooling: the change in temperature of two bodies in thermal contact is proportional to their difference in temperature.
   • Newton's Laws of motion: statements about how large objects made of atoms behave when moving at low speeds relative to each other.
   • The Laws of Thermodynamics: statements about entropy, temperature, and thermal equilibrium.
   • Ohm's Law: the voltage across a purely resistive element is equal to the current through the element times its resistance.
6. Discuss how theories are made and evolve. First, a theory is constructed from facts; fact precede and inform a theory. Secondly, theories contain laws, but laws mean very little without supportive facts. Theories also contain logical inferences.
   • For example, one must infer that the derived laws actually predict the facts. Accumulating all of the previous forms of knowledge, a scientist makes a general statement to explain all the evidence.
   • Other scientists reaffirm the facts and use the theory to make predictions and obtain new facts.

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