物自體 (康德)

物自體，或自在之物（德語：Ding an sich；英語：Thing in itself）是康德所介紹的概念。物自體是獨立於觀察的客體。這個概念在哲學家中間產生了很多爭論。^[1]

康德

康德認為所有客體的總和，也就是這個經驗的世界，它的存在是經先天認知形式（決定其以表象（representation）方式呈現）連結至認知主體。康德對物自體的介紹如下:

And we indeed, rightly considering objects of sense as mere appearances, confess thereby that they are based upon a thing in itself, though we know not this thing as it is in itself, but only know its appearances, viz., the way in which our senses are affected by this unknown something.^[2]

（事實上，既然我們有理由把感官對象僅僅看做是現象，那麼我們就也由之而承認了作為這些現象的基礎的自在之物，雖然我們不知道自在之物是怎麼一回事而只是知道它的現象，也就是只知道我們的感官被這個不知道的什麼東西感染的方式。^[3]）

雅各比

第一個對物自體概念提出批判的是弗里德里希·海因里希·雅各比，他這樣認為：

I could not enter into the system without the assumption of the concept of the thing-in-itself and, on the other hand, I could not remain in it with this concept.^[4]

（在沒有對物自體概念的假設之下，我無法進入這個體系；另一方面，我也無法和這個概念一起待在這個體系里。）

Gottlob Ernst Schulze

匿名出版的《埃奈西德穆》（英語：Aenesidemus (book)）成功給了康德以致命的一擊，根據康德的說法，物自體無法導致現象，因為因果律的範疇只能運用在經驗的客體上。因此康德也無法宣稱物自體的存在。此書後來表明正是G. E. Schulze（英語：Gottlob Ernst Schulze）所著。

這個矛盾後來也被接受為是物自體這個概念存在的主要問題。這本書與此書對物自體的一擊對費希特產生了巨大影響。叔本華稱G. E. Schulze為康德所有對手中最犀利的一位。^[5]

約翰·戈特利布·費希特

起初，費希特很贊同康德哲學，包括物自體的概念，但是Schulze的書改變了他的觀點。

Aenesidemus, which I consider one of the most remarkable products of our decade, has convinced me of something which I admittedly already suspected: that even after the labors of Kant and Reinhold, philosophy is still not a science. Aenesidemus has shaken my own system to its very foundations, and, since one cannot live very well under the open sky, I have been forced to construct a new system. I am convinced that philosophy can become a science only if it is generated from one single principle, but that it must then become just as self-evident as geometry.^[6]

（《埃奈西德穆》，我認為它是我們這個時代最為傑出的作品，它加深了我的懷疑：即便是經過康德和萊茵霍爾德的努力，哲學依舊不是一門科學。《埃奈西德穆》動搖了我的體系中最基礎的部分並使它分崩離析。因為沒有人能在毫無遮蔽的天空下活得很好，所以我被迫建立一個新的體系。我相信哲學能成為一門科學，只要它能從一個簡單的原則開始，那麼這個原則就必須跟幾何學一樣自明了。）

叔本華

儘管叔本華贊同對康德物自體概念的批判，認為康德引入物自體的方式是不可接受的，但是叔本華還是贊同康德對物自體存在的宣稱，並認為康德區分物自體和現象是他最偉大的功績。^[5]

Philipp Mainländer

Mainländer（英語：Philipp Mainländer）的觀點較為特別，他稱頌康德打破了他自己原來的哲學規則，Mainländer也認為物自體是存在的。

He did it, because he feared nothing more than the allegation, that his philosophy is pure idealism, which makes the whole objective world into illusion and takes away all reality from it. The three remarks of the first part of the Prolegomena are, with this in mind, very much worth reading. I cannot condemn this great inconsequence. It was the smaller one of two evils, and Kant bravely embraced it.^[7]

（他這麼做，是因為他毫無畏懼，唯獨懼怕認為他的哲學是純粹唯心論的指控，這個指控會使整個客觀世界陷入錯覺之中，並把它的真實性完全剝離。帶著這樣的想法，《未來形上學導論》第一部分的三篇注釋就變得十分值得拜讀了。我無法指責這偉大的邏輯上的不連貫。二者皆害，此害較輕，康德勇敢地接受了它。）

引用

^ Thielke, Peter; Melamed, Yitzhak. Salomon Maimon. Zalta, Edward N. (編). The Stanford Encyclopedia of Philosophy Fall 2015. Metaphysics Research Lab, Stanford University 「Perhaps the most obvious problem — and certainly one of the earliest — that Kant faces concerns the issue of the thing in itself.」. 2015 [2018-02-10]. （原始內容存檔於2020-06-04）.
^ Kant Immanuel. Prolegomena to Any Future Metaphysics. : § 52c.
^ 伊曼努爾·康德, 龐景仁譯. 任何一种能够作为科学出现的未来形而上学导论. 商務印書館. 1997-4: 86. ISBN 9787100017985. 請檢查|date=中的日期值 (幫助)
^ S. Atlas. From Critical to Speculative Idealism. : p. 21.
^ ^5.0 ^5.1 Arthur Schopenhauer. The World as Will and Representation.. Kant’s greatest merit is the distinction of the phenomenon from the thing in itself … This defect, as is known, is the introduction of the thing in itself in the way chosen by him, the inadmissibleness of which was exposed at length by G. E. Schulze in "Aenesidemus " and was soon recognised as the untenable point of his system. … It is most remarkable that one of Kant’s opponents, and indeed the acutest of them, G. E. Schulze …. : Vol. 1 Criticism of the Kantian Philosophy.
^ Fichte. Early Philosophical Writings. Cornell University Press. 1993: p 4.
^ Philipp Mainländer. Die Philosophie der Erlösung. "Er that es, weil er Nichts mehr fürchtete als den Vorwurf, seine Philosophie sei der reine Idealismus, welcher die ganze objektive Welt zu Schein macht und ihr jede Realität nimmt. Die drei Anmerkungen zum ersten Buche der Prolegomena sind, in dieser Hinsicht, sehr lesenswerth. Diese große Inconsequenz kann ich nicht verdammen. Sie war das kleinere von zwei Uebeln, und Kant ergriff es herzhaft.". : p. 438.

[1] Thielke, Peter; Melamed, Yitzhak. Salomon Maimon. Zalta, Edward N. (編). The Stanford Encyclopedia of Philosophy Fall 2015. Metaphysics Research Lab, Stanford University 「Perhaps the most obvious problem — and certainly one of the earliest — that Kant faces concerns the issue of the thing in itself.」. 2015 [2018-02-10]. （原始內容存檔於2020-06-04）.

[2] Kant Immanuel. Prolegomena to Any Future Metaphysics. : § 52c.

[3] 伊曼努爾·康德, 龐景仁譯. 任何一种能够作为科学出现的未来形而上学导论. 商務印書館. 1997-4: 86. ISBN 9787100017985. 請檢查|date=中的日期值 (幫助)

[4] S. Atlas. From Critical to Speculative Idealism. : p. 21.

[:0-5] 5.0 ^5.1 Arthur Schopenhauer. The World as Will and Representation.. Kant’s greatest merit is the distinction of the phenomenon from the thing in itself … This defect, as is known, is the introduction of the thing in itself in the way chosen by him, the inadmissibleness of which was exposed at length by G. E. Schulze in "Aenesidemus " and was soon recognised as the untenable point of his system. … It is most remarkable that one of Kant’s opponents, and indeed the acutest of them, G. E. Schulze …. : Vol. 1 Criticism of the Kantian Philosophy.

[6] Fichte. Early Philosophical Writings. Cornell University Press. 1993: p 4.

[7] Philipp Mainländer. Die Philosophie der Erlösung. "Er that es, weil er Nichts mehr fürchtete als den Vorwurf, seine Philosophie sei der reine Idealismus, welcher die ganze objektive Welt zu Schein macht und ihr jede Realität nimmt. Die drei Anmerkungen zum ersten Buche der Prolegomena sind, in dieser Hinsicht, sehr lesenswerth. Diese große Inconsequenz kann ich nicht verdammen. Sie war das kleinere von zwei Uebeln, und Kant ergriff es herzhaft.". : p. 438.

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