I'm reading critique of pure reason, from Immanuel Kant:

Now, in the first place, if we have a proposition which contains the idea of necessity in its very conception, it is a¹ if, moreover, it is not derived from any other proposition, unless from one equally involving the idea of necessity, it is absolutely priori.

I have no clue of what he wants to tell me with this, can you help me?

1 - I guess this is an error, may it's "as if".

3 Answers 3


Are you attempting to read the Critique of Pure Reason on your own, outside of a philosophy class?

If so, I'd strongly suggest against doing so, unless you already have a very good background in philosophy. Your question about "necessity" would tend to indicate that this is not the case.

In any event-- the answer to your question is in the sentence preceding the one you quoted: the notion "that it could not possibly exist otherwise."

  • Yes, I'm reading outside a philosophy course but I have interest on the subject, what introduction to philosophy would you suggest me? I have this one.
    – Red Banana
    Commented Jun 30, 2012 at 1:22
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    Is this the Critique the first primary text of philosophy you are trying to read? If so, I'd suggest you start with something easier (and shorter), like Descartes's Meditations. I'm afraid I'm not the best person to recommend an introduction to philosophy, but that would probably be a great question to ask on this site. Commented Jun 30, 2012 at 11:48
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    @GustavoBandeira: I can only assume that the education Einstein had must have prepared him for the task. As for the similar questions-- do the answers there help you? If so, no need to ask it again. Commented Jul 1, 2012 at 10:22
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    There are some nice guides to the Critique, which will help step you through the text-- but to understand the ideas at stake, you'll also need a good overview of the tradition from Descartes up to Kant. Commented Jul 1, 2012 at 13:39
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    If you are new to philosophy as a whole, get a general intro philosophy book. Read that fully, then if you still want to get into Kant, at least try reading Prolegomena to Any Future Metaphysics before diving right into the Critique. See Which of Kant's writings would be a good introduction to his work?
    – stoicfury
    Commented Jul 2, 2012 at 10:43

As pointed out by @MichaelDorfman, the definition of "necessary" is "that it could not possibly exist otherwise". A good example on this that might help you out is the relation between color and extension. You cannot have color without extension, as such, there's a relation of necessity between them. (But, as pointed by @JosephWeissman, you could have extension without color).

A similar and popular example is "All bodies are extense (take up space)", as you cannot have a body without extension, extension is necessary for the conception of a body. As the predicate is a necessary condition for the concept of the subject, this statement is what Kant calls an analytic proposition.

A proposition like this indicates what is the concept about. Consider "A square has four equal sides". It is necessary for some object to be called "square" to have "four equal sides and four equal angles". If you say "this square is big/small/red/black", these are not necessary conditions, only possible ones, they do not affect the concept of a square. This is pretty much like what is called "accidental" in philosophy - the accidental characters (color/size) do not change the fact that it is a square. This is why Kant considers necessity an "a priori" knowledge, it is beyond sensorial experience, otherwise you could not call so many different objects a "square".

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    Interesting point, but just physically speaking -- doesn't a particle or atom 'extend' without having an identifiable color (being smaller than the wavelengths of the colored light spectrum)?
    – Joseph Weissman
    Commented Jun 30, 2012 at 0:12
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    @JosephWeissman I guess you are right, possibly I'd have to say that you cannot have color without extension, but you can have extension without color?
    – Tames
    Commented Jun 30, 2012 at 1:03
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    @GustavoBandeira yes.. it occupies "space", even if it is just projected light
    – Tames
    Commented Jun 30, 2012 at 2:31
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    @GustavoBandeira this example comes from Berkeley, actually
    – Tames
    Commented Jun 30, 2012 at 2:32
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    @GustavoBandeira I added some extra information. Please let me know if there's something needed to clarify it further.
    – Tames
    Commented Jul 1, 2012 at 14:18

I began studying the Critique 35 years ago. I am still studying. Be careful when reading critical analysis by others who claim authority on Kant's Critique or Prolegomena. Research whether they are pro or anti Kant - however tacit.I am not suggesting how to select, only be aware that even philosophers can be sceptics, dogmatists, realists, idealist or a bit of each. I will emphasize a previous suggestion that before attempting Kant you should have a thorough handle on philosophic terminology and concepts, analytics, logic and some history from at least Descartes to Kant. Roger Scruton's 'Modern Philosophy' comes highly recommended. Plus there is GOOGLE, an Invaluable resource. Choose your reading material carefully or you will find yourself wandering aimlessly down dark dead end alleys lost and confused wandering in circles cul-de-sac after cul-de-sac wasting vast amounts time getting nowhere.

Authors to consider : (5)Allison -'Transcendental Idealism' (defends T.I with reservations)

(1)Gardner -'Kant and The Critique of Pure Reason' (Excellent Guidebook)

(6)Grier- 'Kant's Doctrine of Transcendental Illusion'- In defence of -

(7)Stern - Transcendental Arguments and Scepticism (Negative)

(4)Strawson - 'The Bounds of Sense'(Common Sense REALIST-anti T.I)

(8)Langton-'Kantian Humility'- Epistemic vs metaphysical a-priori knowledge

(3)Guyer- Kant(Routledge)- Subtle negativity on many Kantian premises.

(2)Guyer-The Camebridge Companion To Kant- 14 essays by different authors

(9)Guyer-Kant and the claims of knowledge- Confused representation of Kant's 'refutation'-Idealism and Realism (Epistemology)

I found Gardner's Guidebook the best starter. From there the choice of paths to comprehending the depth and breadth of Kant is yours. It is an addiction. Lifetimes have been spent in this study. Tread carefully. It all depends on how much time you have, how much patience and determination you have and how much you are 'awed' by the unparalleled genius of Emanuel Kant.

These opinions and suggestions are mine and come from personal experience. Other suggestions and criticisms must be equally considered as I do not claim to be an authority on Kant, only a guest.

The numbers in front of the book suggestions indicate the order I read them in. There are countless others that could be read aside from these.

I do think GARDNER is by far the BEST place to start. This is not to suggest you do the same.

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    Welcome to Philosophy.SE. This sounds like helpful advise in general, but doesn't seem to answer the question as such. Could you perhaps edit to focus on that as well?
    – user2953
    Commented Aug 23, 2017 at 14:23

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