Jacobson (in Basic Algebra $1$) defines a separable polynomial to be one whose irreducible factors have distinct roots. Then he defines a perfect field to be a field $F$ such that every polynomial in $F[x]$ is separable, and proves that if $F$ is finite or of characteristic $0$, then it is perfect.
At the beginning of the section corresponding to this, he says:
We shall show in this section that if $F$ is of characteristic $0$ or if $F$ is a finite field, then there is no loss in generality in assuming that all the roots are simple.
I don't understand what this is supposed to mean. What is the "generality" in which there is no loss with that assumption?
This section starts at page $229$. The quote is the first sentence on page $230$.