Why study the History of Philosophy?

In the book " A history of Philosophy", Fredrick Copleston, SJ stated three reasons to why a student of Philosophy should study its history.

The first reason is that Philosophy grew out from the past. This means that the thoughts of the past philosophers contributes to the thoughts of the present or the latter philosophers. A modern philosopher's philosophy did not just emerge solely from him/her. These ideas are influenced by some other philosophers or thinkers. If one aims to know and understand better the philosophy of one philosopher, he/she then must know and understand the philosophies that influenced that philosopher. The influence can only be determined through studying or checking the background of the philosopher and the philosophies. Therefore studying history lets a person understand more the idea that created an impact to the modern philosopher.

The second reason is to avoid repeating the mistakes done by the previous philosophers. This is to say that there are ideas from the past that may not be entirely enough to the present situation. It may be that the philosophy lacks something. Studying the history of Philosophy will inform the modern philosopher that a certain idea has been thought of and that the account has insufficient premises that supports the main idea. Therefore, studying the history or the past lets a modern philosopher correct, refute, support, and add the philosophy of the past philosopher.

The third reason is that an idea is growing and developing through time. This means that a philosopher's idea today can be modified by tomorrow's philosopher. This is to say that no philosophy is stagnant and is fixed. A philosophy is developed as there would always be new facts and new situations. But the developing of the philosophy does not mean that there is something wrong in it. It only implies that there are new findings, and new thoughts that can better suit the situation. Therefore, there is a need to study history because no philosophy is fixed and the philosophy of the old philosophers continues to connect in the present situation thus it can help in the new discoveries.

According to Fredrick Copleston, there is a need to study the history of Philosophy as it grew from the past, as it lets the new philosophers avoid repeating the mistakes done by the previous philosophers, and as it grows and develops through time.

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Source
Copleston, F.1993.A History of Philosophy Vol. 1.New York; Doubleday.