Why murphy's law and not murphy law

Cabeza tuna

Senior Member
Chilean Spanish & Chilean Coa
I have a question for you and I really appreciatte your help, I always ask me why you have to put an 's after the names for example
Murphy's law,Mcdonald's ,etc.
There is any reason for that? is a rule? when I have to use it ?
Thanks I know than my english is not so good but I am doing my best to improve it.
  • JamesM

    Senior Member
    The "'s" indicates possession. Murphy (whoever he was) made up the law called Murphy's Law. McDonald's is short for McDonald's Restaurant, the restaurant started by Mr. McDonald. It is the same for Einstein's Theory of Relativity or Planck's Constant (although that is also referred to as the Planck Constant.)

    To me, the Murphy Law would be a law that applied to people named Murphy, if such a thing were possible, like the Child Labor Law.

    I can see where it would be confusing. I don't know of a rule other than whether or not something is applying to someone or owned/invented/created by someone. I imagine that is as much a cultural interpretation as anything so I don't know that it helps in any way.

    There are many ESL teachers on the board. Perhaps one of them has learned a useful rule of thumb for this.


    Senior Member
    USA English
    Adding a note to JamesM's explanation (note the possessive), from time to time, you will see the apostrophe omitted so as to make names consistent. For example, the apostrophe is usually, if not always, omitted in the names of U.S. cities and street names.
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