In a description of David Hume, examples of a priori and a posteriori are given:

a posteriori: "Dogs are carnivores"
a priori: "Bachelors are unmarried"

I am having trouble differentiating between the two statements. "Bachelors are unmarried" is a priori because I know that the definition of Bachelor is unmarried man. But what if I am perfectly versed in the English language, but have, for whatever reason, never encountered the word Bachelor. I do not know that a Bachelor is unmarried. In order for me to find out if a Bachelor is unmarried I must make an observation (like opening a dictionary.) Likewise for "Dogs are carnivores", I know that dogs also eat other stuff apart from meat so I don't need to make an observation, which would mean the statement is for me a priori.

So have I misunderstood the difference between a priori and a posteriori, or are these terms dependent on the individual's already acquired knowledge? Can a statement be a priori for one person and a posteriori for another person?

  • 2
    If you never encountered modern-day numerals it wouldn't make 1+1=2 any less true.
    – anon
    Aug 23, 2011 at 17:48

3 Answers 3


A posteriori simply means that someone would have had to experience it in order to acquire that knowledge. E.G. "Dogs are carnivores". The notion that Dogs are carnivores is not contained in the definition of a dog. When the first dog was encountered by the very first man on this planet, he could not for sure say "dogs are carnivores". He wouldn't know until he observed their eating habits. It required experience.

A priori, on the other hand, means that you can know the idea independent of having to experience it. Typically, the definition of the word is contained in the statement you are examining. E.G. "Bachelors are unmarried." The person who invented the term "bachelor" did not have to go outside and find a bachelor and proclaim "hey! You sir, are unmarried. Therefore all bachelors are unmarried". The very term was defined that way. It required no experience to know that.

There is really no place for subjectivity/objectivity here. You might consider looking up some distinctions which are relevant, however, such as Kant's analytic-synthetic distinction and others, which might mitigate your confusion.

  • 1
    Thank you; I still have some reservations, but I'm still finding my way. I had looked at the "others" link. Your answer makes it clearer. It is my intention anyway to read alot more.
    – leancz
    Aug 23, 2011 at 14:06
  • 1
    Good to hear! If you want to be a good philosopher, it is always beneficial to be a good reader too :)
    – stoicfury
    Aug 24, 2011 at 1:35
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    I would like to add a link to the best explanation I have yet read: iep.utm.edu/apriori
    – leancz
    Oct 30, 2012 at 14:26

To add to stoicfury's answer, you want to separate out what parts of a statement are taken to be a priori and what a posteriori; some of this is a bit of the game we're playing.

It does seem like for you the 'bachelor is unmarried' is a posteriori because you may not yet know the definitions of the words. But that just means that definitions are themselves a posteriori. You must get the definitions from experience (or have them stipulated by authority. The statement about bachelors and marriedness is still a priori (derivable without experience) because this game assumes the definitions are already made (you're not trying to figure out the definition of 'bachelor' from this particular statement).

A similar analysis works for 'Dogs are carnivores': the game stipulates that you already know the definition of 'dog' and 'carnivore' and that 'dog' doesn't necessarily imply 'carnivore'.


Understanding what a claim is actually claiming is logically prior to determining if the claim is true or false. The terms "a priori" and "a posteriori" refer to how you determine if the claim is true, not how you come to understand the claim.

We use words to name concepts. Claims consists of concepts, but are phrased in words when we need to communicate them to others. When evaluating the truth of a claim, no communication with others is involved, only the internal manipulation of concepts is involved.

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