From Philosophy.com
The relationship between logic and psychology was fought over most intensely in the German-speaking lands between 1890 and 1914. Indeed, during this period pretty much all of German-speaking philosophy was engulfed in the so-called Psychologismus-Streit (the ‘psychologism dispute’). This dispute centered on the question whether logic (and epistemology) are parts of psychology. Gottlob Frege and Edmund Husserl are the best-known figures of this controversy. The fact that the psychologism dispute has become closely associated with German-speaking philosophy must not, however, blind us to the enormous influence of John Stuart Mill upon both sides of the controversy. Paradoxically, Mill’s Logic of 1843 was not only a key inspiration behind much German-speaking psychologistic philosophy, it also contained some crucially important anti-psychologistic ideas.

In what follows, I shall begin with a short summary of Mill’s contribution. Subsequently, and turning to the German scene, I shall briefly sketch what authors accused of psychologism said on the relationship between logic and psychology, before outlining Frege’s and Husserl’s arguments against them. I shall conclude by presenting a number of objections to Frege’s and Husserl’s anti-psychologism. Some of these objections come from Frege’s and Husserl’s contemporaries, others are of more recent origin.

Comments by Mr Someone:

THE ABSTRACT philosophies of the modern world have had this queer twist. Since the modern world began in the sixteenth century, nobody’s system of philosophy has really corresponded to everybody’s sense of reality; to what, if left to themselves, common men would call common sense. Each (modern philosophy) started with a paradox; a peculiar point of view demanding the sacrifice of what they would call a sane point of view. That is the one thing common to Hobbes and Hegel, to Kant and Bergson, to Berkeley and William James. A man had to believe something that no normal man would believe, if it were suddenly propounded to his simplicity; as that law is above right, or right is outside reason, or things are only as we think them, or everything is relative to a reality that is not there. The modern philosopher claims, like a sort of confidence man, that if once we will grant him this, the rest will be easy; he will straighten out the world, if once he is allowed to give this one twist to the mind.”