grammar - Is *a* optional after *both*?

This is a quote from a book:

Leibniz was both philosopher and mathematician.

To me it should be "both a philosopher and (a) mathematician." Is the article a optionall after both? Does both includes a?

Answer

If he is just one of them:

Leibniz was a philosopher.

then a is necessary. But when he is both:

Leibniz was both philosopher and mathematician.

then he is two things (philosopher and mathematician), so a is not appropriate.
However, as you mentioned you could say;

Leibniz was both a philosopher and a mathematician.

which treats each one separately. I believe this would be technically correct.