Frege's Criticism of Psychologism

According to psychologism, laws of logic and mathematics are not anything except generalized accounts of thought patterns which govern human's mind. Therefore, the content of laws of logic is merely subjective idea created by the human mind. If the structure of the mind was different from our actual structure, then the laws of logic would be something different from the laws existing now. For Frege, this theory is on the basis of the conceptualism and idealism of the meaning of the words. Frege believes that the meanings of propositions, which he called "Thought", are a distinct matter from "Ideas", which exist in every individual's mind. Frege's arguments endeavor to prove it via two basic reasonings, as stated in this article. The absence of common discourse, which changes language to an individual matter, as well as the presentation of "epistemological relativism" are two vicious consequences, which is the course of accepting the matter that there is no distinction between "Thought" and "Idea". In Frege’s view, if psychologism were true, everything would be reduced to "Idea". And if everything reduces to "Idea", "Thought" will be "Idea" as well; however, "Thought" is not "Idea". Therefore, psychalogism is void. When Frege tries to explain why Thought is not the same as Idea, he starts with the Idea properties. Frege believes that Ideas are dependent on individual (Individual-dependent), and are always dependent, hence, cannot exist without their owner independently. Each Idea only belongs to one person (individual) can never be the owner of another’s Idea. Our own Ideas naturally and essentially are so related to our consciousness realm that each Idea owned by every person is distinct from our own Idea only belonging to ours. If two persons have one Idea, it is necessary that Ideas exist independently from them, which is in contrast to the hypothesis and essence of Idea.
In his first arguments, Frege declares that if Thought is the same as Idea, it would not be possible to have common perception about one Thought, therefore, identical meaning, and as a result conversation (common discourse), would not exist. So, language would change into an individual private matter. This outcome is a result of individual-dependent (relative to subjects) relative to characteristic of Idea.
His second argument is in the same direction as the first one, stating that if Thought is the same as Idea, contradiction between two Thoughts would not be possible. Because there is no identical criterion by which people (person who are communicating) could evaluate their perception, verify the validity of their viewpoints, and discover the contradiction of their thoughts toward others. Also, dispute over Truth would be vain. It is like the quarrel between two persons who fight over being an original 100 Marks banknote in their pocket. Each of them believes that only the banknote in his/her own pocket is original, then all the science would not be only as superstition.
Frege in his second arguments illustrate that epistemological relativism and individualism are vicious consequents of psychologism.
This research investigates the criticism of some classic logicians and contemporary thinkers on Islamic philosophy. They have declared that Frege does not distinguish between conceptualism and psychologism and also between existence of Idea and its indication. Moreover, they criticize Frege's affirmative theory about grasping of thought.
In this research, it becomes clear that Frege's objections to conceptualism (psychological individualism) are still valid. There is no convincing reply to these objections yet. The approach of this research concentrates on the Frege's negative reasoning in the criticism of psychologism, not on the Frege’s affirmative views on the manner of Thought perceptions