Language is an instrument of Logic, but not an indispensable instrument.
Boole 1847a, 118
We know that mathematicians care no more for logic than logicians for mathematics. The two eyes of exact science are mathematics and logic; the mathematical sect puts out the logical eye, the logical sect puts out the mathematical eye; each believing that it sees better with one eye than with two.
De Morgan 1868a, 71
That which is provable, ought not to be believed in science without proof.
Dedekind 1888a, preface
If I compare arithmetic with a tree that unfolds upwards in a multitude of techniques and theorems whilst the root drives into the depths […]
Frege 1893a, xiii
Arithmetic must be discovered in just the same sense ...