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 ...

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