Full Idea
If some law which has no exceptions applies to a case, we can never be sure that we have discovered that law and not one to which there are exceptions; also the reign of law would seem to be itself only probable.
Gist of Idea
We can't know that our laws are exceptionless, or even that there are any laws
Source
Bertrand Russell (Problems of Philosophy [1912], Ch. 6)
Book Reference
Russell,Bertrand: 'The Problems of Philosophy' [OUP 1995], p.36
A Reaction
None of this can be denied. In modern physics, several supposed laws have come up for question. Is the proton stable? Are the gravitational constant or the speed of light necessarily fixed? Russell is doing epistemology. How do we conceive the laws?