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Difference between Theory and Law

Theory vs Law

Theory and law are interrelated. It is a common misconception that these two may be used alternatively. Now let us take a look at each one in detail.

According to science, a law is a generalized statement set after a number of observations. A law has no explanations or exceptions when it is framed. It is an obvious fact recorded after observations.
A good example of this may be the force of gravity. It is observed that an apple falls down on the surface of the Earth. It is an undeniable fact. This observation has no exceptions also. No one has ever observed a reverse or alternative phenomenon. Hence it is considered to be a law.
There is another misconception about the hierarchical level of law. A group of scientists is of the idea that there is a hierarchy of hypothesis, theory, and law, but this is only an erroneous statement. Laws are obvious and simple statements.

A theory is the explanation of the observational data set forward in the form of a law. In simple words, a theory is the reasoning behind a law. It may also be put as an advanced or evolved hypothesis. “Hypothesis” is a probable reason behind any observation. A hypothesis has to undergo various tests. If the hypothesis holds well in different conditions, it may be accepted as a theory.

Taking account of the previous example of the law of gravity, in 1687 Sir Isaac Newton put forward the inverse square law in his journal. It was till then a hypothesis. This law was put to a test by different scientists in the study of planetary motion. With some of the planets the hypothesis held good but exceptions were there. At this stage, Newton’s hypothesis was accepted as a theory, “the gravitational theory.” This theory was later superseded by Einstein’s Theory of Relativity.

A theory can be a strong one if it has a lot of evidence to back it. It may also be regarded as a weak theory if the amount of accuracy in its prediction is low. A theory may become obsolete with time and be replaced by a better one. A law, however, is a universally observable fact. It is undeniable and never fades away with the stretch of time.


1.A law is an observation; a theory is the explanation of that observation.
2.A theory requires experimentation under various conditions. A law has no such requirements.
3.A theory may become obsolete with time. This is not the case with a law.
4.A theory can be replaced by another better theory; however, this never happens with a law.
5.A theory may be strong or weak according to the amount of evidence available. A law is a universally observable fact.

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  1. Sir,i want knw that can we say a theory as law

  2. The explanation is concise and easy to understand. Although I would recommend a change. Laws can have exception as well as theories. For instance, the ideal gas law has many exceptions that vary from the precise behavior dictated by the law.
    Please see this article by the University of California Berkley for a citation of this. Berkley is, undoubtedly, a credible source in this matter.

    • I disagree with your statement about exceptions to the ideal gas law. As the article you reference explains, there are no ideal gases, the law is not an observation of ideal gases. The law defines an ideal gas. This law is useful in approximating REAL gas behaviors. gases approach this behavior when they are at less than 2x atmospheric pressure and more than (if I recall correctly) 2x their critical temperature. Assuming ideal gas behavior tends to be remarkably accurate (often less than 10% error) at pressures in the thousands of psi and in engineering greatly simplifies polytropic and supersonic calculations to within known tolerances.

      There are no ideal gases, so no ideal gas is observed to be an exception to the law.

  3. If hypothesis is falsefied by the experiment it becomes theory

    If hypothesis is not falsefied by the experiment it becomes law

    • I love your synopsis. I was surprised by the articles statement that a law will always be true, and that there is no hierachy between hypothesis, theory, and law. This despite mentioning a hypothesis can become theory. I see a hierarchy in “not sure, but might be true”, “true most of the time”, and “universally true for all cases and for all time.” But hey, I’m an engineer not a doctor.

  4. If a theory can be rejected or not?

  5. In the early 20th century, we have Einstein’s Theory of Relativity, Quantum Theory, there are all these theories, we no longer use the term “Law” to describe the conduct of nature. They are for several reasons. First, these “Theories” are as well tested and as successful as those “Laws”, so we could call them laws if we want to so that it would be consistent with the past generations. But what happens during the early 20th century was we came to learn that whatever it is we determined to be true about nature may only be a subset of a larger truth (i.e. Newton’s Law of motion describes the behavior of matter under low gravity, yet fail to demonstrate it for velocity near the speed of light; Einstein’s “Theory” took over for describing in higher velocity), but it doesn’t discard the preceding law, instead, enhancing our understanding over which the law applies. So, in the modern time, if we call a well tested hypothesis as a theory, back in the 18th century they would be calling that the law. Just in case you wonder, experimentally verified theories does not get rejected or overturned, our understanding will only be enhanced by more discoveries that we do in understanding the conduct of nature.
    -From “Just an engineer”

  6. Thanks for stating it in such a clear way.

  7. I need help pleases.

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