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Chemistry LibreTexts

1.3: Hypothesis, Theories, and Laws

[ "article:topic", "hypothesis", "law", "Theory", "showtoc:no" ]
  • Page ID
    47443
  • Skills to Develop

    • Describe the difference between hypothesis, theory as scientific terms.
    • Describe the difference between a theory and scientific law.

    Although all of us have taken science classes throughout the course of our study, many people have incorrect or misleading ideas about some of the most important and basic principles in science. We have all heard of hypotheses, theories, and laws, but what do they really mean? Before you read this section, think about what you have learned about these terms before. What do these terms mean to you? What do you read contradicts what you thought? What do you read supports what you thought?

    What is a Fact?

    A fact is a basic statement establish by experiment or observation. All facts are true under the specific conditions of the observation.

    What is a Hypothesis?

    One of the most common terms used in science classes is a "hypothesis". The word can have many different definitions, depending on the context in which it is being used:

    • "An educated guess" - because it provides a suggested solution based on evidence to be a scientific hypothesis
    • Prediction - if you have ever carried out a science experiment, you probably made this type of hypothesis, in which you predicted the outcome of your experiment.
    • Tentative or Proposed explanation - hypotheses can be suggestions about why something is observed, but in order for it to be scientific, we must be able to test the explanation to see if it works, if it is able to correctly predict what will happen in a situation, such as: if my hypothesis is correct, we should see ___ result when we perform ___ test.

    A hypothesis is very tentative; it can be easily changed.

    What is a Theory?

    The United States National Academy of Sciences describes what a theory is as follows:

    "Some scientific explanations are so well established that no new evidence is likely to alter them. The explanation becomes a scientific theory. In everyday language a theory means a hunch or speculation. Not so in science. In science, the word theory refers to a comprehensive explanation of an important feature of nature supported by facts gathered over time. Theories also allow scientists to make predictions about as yet unobserved phenomena."

    "A scientific theory is a well-substantiated explanation of some aspect of the natural world, based on a body of facts that have been repeatedly confirmed through observation and experimentation. Such fact-supported theories are not "guesses" but reliable accounts of the real world. The theory of biological evolution is more than "just a theory." It is as factual an explanation of the universe as the atomic theory of matter (stating that everything is made of atoms) or the germ theory of disease (which states that many diseases are caused by germs). Our understanding of gravity is still a work in progress. But the phenomenon of gravity, like evolution, is an accepted fact."

    Not some key features of theories that are important to understand from this description:

    • Theories are explanations of natural phenomenon. They aren't predictions (although we may use theories to make predictions). They are explanations why we observe something.
    • Theories aren't likely to change. They have so much support and are able to explain satisfactorily so many observations, that they are not likely to change. Theories can, indeed, be facts. Theories can change, but it is a long and difficult process. In order for a theory to change, there must be many observations or evidence that the theory cannot explain.
    • Theories are not guesses. The phrase "just a theory" has no room in science. To be a scientific theory carries a lot of weight; it is not just one person's idea about something

    Theories aren't likely to change.

    What is a Law?

    Scientific laws are similar to scientific theories in that they are principles that can be used to predict the behavior of the natural world. Both scientific laws and scientific theories are typically well-supported by observations and/or experimental evidence. Usually scientific laws refer to rules for how nature will behave under certain conditions, frequently written as an equation. Scientific theories are more overarching explanations of how nature works and why it exhibits certain characteristics. As a comparison, theories explain why we observe what we do and laws describe what happens.

    For example, around the year 1800, Jacques Charles and other scientists were working with gases to, among other reasons, improve the design of the hot air balloon. These scientists found, after many, many tests, that certain patterns existed in the observations on gas behavior. If the temperature of the gas is increased, the volume of the gas increased. This is known as a natural law. A law is a relationship that exists between variables in a group of data. Laws describe the patterns we see in large amounts of data, but do not describe why the patterns exist.

    What is a Belief?

    A statement that is not scientifically provable. Beliefs may or may not be incorrect; they just are outside the realm of science to explore.

    Laws vs. Theories

    A common misconception is that scientific theories are rudimentary ideas that will eventually graduate into scientific laws when enough data and evidence has been accumulated. A theory does not change into a scientific law with the accumulation of new or better evidence. Remember, theories are explanations and laws are patterns we see in large amounts of data, frequently written as an equation. A theory will always remain a theory; a law will always remain a law.

    Video \(\PageIndex{1}\): What’s the difference between a scientific law and theory?

    Summary

    • A hypothesis is a tentative explanation that can be tested by further investigation.
    • A theory is a well-supported explanation of observations.
    • A scientific law is a statement that summarizes the relationship between variables.
    • An experiment is a controlled method of testing a hypothesis.

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