# English grammar in physics

Gold Member
What is correct, Einstein equation or Einstein's equation? Newton law or Newton's law? Allegedly the correct answers are Einstein equation and Newton's law, but that doesn't seem logical to me. What is the general rule?

Useful nucleus

Gold Member
Grammatically should be

' the Einstein equation ' or ' Einstein's equation ' .

' the Newton laws ' or ' Newton's laws '

If referring to a specific law of the set then :

' the second Newton law ' or ' Newton's second law ' or ' the second of Newton's laws ' .

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UsableThought, cnh1995 and Demystifier
Gold Member
Grammatically should be

' the Einstein equation ' or ' Einstein's equation ' .

' the Newton laws ' or ' Newton's laws '

If referring to a specific law of the set then :

' the second Newton law ' or ' Newton's second law ' or ' the second of Newton's laws ' .
Makes sense, but recently editors in Elsevier changed my "the Newton second law" into "the Newton’s second law". Are they wrong?

Gold Member
Yes - they are wrong .

English grammar mostly works like mathematics .

The (second ( Newton's ( law ))) is not the same as The ( Newton's ( second ( law )))

The first construction means that you refer to Newton's laws and specifically to the second one . This is clear and correct .

The other construction actually means that you refer to second laws and specifically to Newton's one . At best bad grammar but in a more complex reference could cause multiple ambiguities .

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davenn, Useful nucleus, PeroK and 1 other person
Homework Helper
recently editors in Elsevier changed my "the Newton second law" into "the Newton’s second law". Are they wrong?
Both look wrong to me. Either "Newton's second law" or "the second Newton law". The first is more usual. My impression is that custom dictates "Smith's law" and "the Smith equation", but I don't know if anyone has made this an official rule.
To me, "the second Newton law" implies the second of Newton's laws (as distinct from the first or third); "the Newton second law" implies Newton's second law, as opposed to anyone else's second law (e.g. Mr. Thermodynamics). Or even a law about a quantity with units of N s.
It is definitely bad grammar to put the definite article before an individual's proper name in the genitive. The only example I can immediately think of is "the Young's modulus", which is common usage.

kith and UsableThought
Staff Emeritus
I just got back from a long argument about Green's Functions vs. Green Functions. I wonder what other colors they come in?

Homework Helper
Gold Member
2022 Award
I just got back from a long argument about Green's Functions vs. Green Functions. I wonder what other colors they come in?

Green's windmill:

Green windmill:

Demystifier