Posted by: thebylog | September 19, 2006

Obvious is a Subset of True

There are lots of true statements, some of which are “obvious” and some of which are not. When you’re trying to prove something mathematically and in the course of your proof you want to use some other true statement, if the fact is “obvious” you can simply state it and use it. But if it’s not “obvious” then you have to prove it before you can use it.

The question is, how do you tell when something is “obvious”? Like, I know this certain statement is true, but I either don’t want to or can’t actually prove it rigorously. So I just say it’s “obvious.”

Problem solved.



  1. To be obvious, does the statement have to appear obvious to a reasonably informed person, or need it only be obvious to a student of whatever discipline is being argued?

    Reasonably informed person comes from my auditing class, btw. Thought I would add that for good measure.

  2. so man you must get the lastest edition of sports illustrated. the one with a-rod on the cover. on about the 8th page or so is a pic of the ducks blocking the oklahoma field goal, but as i was looking closer at the picture i noticed in the crowd a redhead. there he is man in sports illustrated! our little bro justin, and dad. i about accidented myself. its rather suprising looking in a magazine and seeing your brother. anyway check it out. i’ll call you tomma.

  3. Myron, I think it needs to be obvious to someone with basic knowledge in the discipline. However, authors skip steps all the time in proofs, assuming students can or will fill in the gaps. That’s what, in my experience, makes reading certain textbooks difficult.

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