Gottlob Frege, answered from the texts and cited to the page.
Logic is not a branch of psychology. The laws of logic are not generalisations about how human beings happen to think; they are laws of truth, normative on thought rather than descriptive of it.1 A Gedanke (Thought) is the Sinn of an assertoric sentence — an objective abstract entity, neither a physical object nor a psychological event nor a Vorstellung (mental image).
Thoughts inhabit a third realm: distinct from the physical world of bodies and from the inner world of mental events, accessible to multiple minds, eternally true or false, independent of being grasped. Two thinkers who grasp the same Thought grasp numerically the same entity; if Thoughts were mental contents, every thinker's "thought that 2+2=4" would be a different thought and shared knowledge would be impossible.
The objectivity of mathematics, the possibility of communication, and the very intelligibility of disagreement all require that Thoughts be objective.234
He can do this because the truth of a thought is timeless. Therefore that truth cannot have come to be only upon its discovery. Not everything is an idea. Otherwise psychology would contain all the sciences within it, or at least it would be the supreme judge over all the sciences. Otherwise psychology would rule even over logic and mathematics.Collected Papers on Mathematics, Logic, and Philosophy, pp. 374–375
Then the cause of this might be that the phosphorus content in the cerebral cortex had changed, and we should then have to say something like 'If the amount of phosphorus present in any part of man's cerebral cortex does not exceed 4%, his judgement will always be in accordance with the law that every object is identical with itself." We can at least conceive of psychological laws that refer in this way to the…Posthumous Writings, pp. 162–163
There would be no science, no error and no correction of error; properly speaking, there would be nothing true in the normal sense of the word. For this is so closely bound up with that independence of being recognized as true, which we are emphasizing here, that it cannot be separated from it.Posthumous Writings, p. 147
There is no way of telling whether Frege also received the other articles. The fifth article is a critical discussion of Anton Marty, Uber subjektlose Sditze und das Verhdltnis der Grammatik zur Logik und Psychologie, 6th and 7th articles, VierteYahrsschrift fiir wissenschaftliche Philosophie X1X (1895), pp. 19-87 and 263-334.Philosophical and Mathematical Correspondence, p. 85
The foundational doctrine of Frege's mature philosophy of mind and language and the locus classicus of 20th-century anti-psychologism. The 1894 review of Husserl's Philosophie der Arithmetik is the most celebrated polemic in the tradition; Husserl himself in the Logische Untersuchungen Prolegomena (1900) developed a convergent anti-psychologism, crediting Frege's critique in part. Tyler Burge's "Frege on Knowing the Third Realm" (1992) is the canonical contemporary defence; his Truth, Thought, Reason (2005) develops the anti-individualist line. Quine's naturalist worries about Platonism, the post-Wittgensteinian rejection of the third realm in some readings of Philosophical Investigations, and the externalist tradition descending from Putnam's "Meaning and Reference" (1973) are the principal contemporary challenges. Most analytic philosophers retain some version of the anti-psychologism even where they refuse the Platonist ontology of the third realm.