Time to be smart: ‘Fact’, ‘Law’, ‘Hypothesis’ and ‘Theory’ in Science.

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I recently watched a youtube video where Dr Zakeer Naik says to a bright medical student that a ‘theory’ in science will only become ‘law’ after testing and verifying its correctness using scientific methods. I got shocked listening to this nonsense. Here is a man with the title ‘Dr’ (physician, I guess) who is supposed to educate himself at least with the scientific terms from his science classes. It seems that there is a lot of people out there who are confused about differences between the terms such as fact, law, hypothesis, and theory. I believe that at least people who work in science-related professions should know the difference.  

Although the terms mentioned above might have multiple meanings in our everyday English vocabulary, in science, they are defined well rigorously. Let’s have a look at those definitions in science:

  1. Fact: It is an observation of a phenomenon/event that has been repeatedly confirmed and finally accepted. It is always true under well-defined conditions/circumstances. E.g.:
    • “When I drop objects, they fall on the ground.”
  2. Hypothesis: A proposed explanation of an observed fact (A hypothesis can become a law or a theory as you will read further down the article). So, a hypothesis need not be right. Let’s see some possible hypotheses on gravity. E.g.:
    • “Some mysterious force-field is located inside the earth. This force continuously attracts every object towards it.”
    • “Every object attracts to each other. So objects fall on the ground as a result of the earth’s attractive force of some kind.”
    • “Not every object attracts to each other, but only earth attracts all other objects. My pencil never seems to get attracted by my pen.”
    • “Every object has its own natural state of rest. This state is acquired when an object is at the centre of the universe. Since the earth is the centre of the universe, objects tend to move towards the earth’s centre!”
  3. Law: A law describes the working principle of a fact. This description never tells us why it works; instead, it only tells us how it works, most often backed up by mathematical equations. E.g.:
    • “A man named Newton sits alone inside his house for years and finally comes out one day, hypothesizing that objects attract each other by a force whose strength depends on their masses and the distance between them. He formulates mathematical equations describing his observation. Independent experimental tests over more than 300 years validate these equations, and people start to consider these as the laws of gravity. All other alternate hypotheses explaining the earth’s attractive nature should be abandoned as they fail all the experiments.”
  4. Theory: A theory explains why an observed fact works. It describes the mechanism involved. A theory can be developed with a set of postulates. The starting point of developing a theory is the proposition of a hypothesis with certain postulates. A hypothesis can become a theory when it is tested and verified scientifically. But no amount of supporting experiments can prove that a theory is 100% accurate because scientists entertain the possibility of corrections in the future. A theory should also pass the experimental observations of all its predictions. If a theoretical prediction contradicts with the experimental observation, the theory should either be modified or corrected. E.g.:
    • Einstein’s general theory of relativity explains why gravity works the way it does. Because of the uneven distribution of mass, the space-time around the mass will be warped, which in turn pushes objects to move along specified paths.
Google’s definition of the word ‘Theory’

No wonder why people mistake the word “Scientific theory ” as “hypothesis”. Internet says “theory” and “hypothesis” are synonyms: 

Often people misinterpret that a ‘scientific theory’ and a ‘theory’ are the same. But they are entirely different in science.

Next time if someone says that ‘Theory of Evolution of species’ is just a theory and wrong at that, then you can confidently ask them to learn first, the meaning of what a scientific theory is. It is time to be smart. 🙂 


  1. The Role of Theory in Advancing 21st Century Biology, National Academy of Sciences
  2. http://oregonstate.edu/instruction/bb317/scientifictheories.html
  3. A great youtube video on this topic explained by Joe Hanson, PhD.

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