It rhymes and wonders: who am I?

Question

I tossed off this quick one. Does that make me a tosser?

I know what is or isn't,
  but never what might be;
And many claim to know me,
  though many disagree;
There are no sly dilemmas,
  no subtleties I see;
Both I encompass gladly,
  to be, and not to be.

It's two long words, but you can use just one, provided it's short.

Answer 1

You said in a comment to think computers, so I did.

A boolean variable.

I know what is or isn't,
but never what might be;

Which is the case with variables. You know what type it is/isn't, but not what its value will end up being.

And many claim to know me,
though many disagree;

Rather vague statement, as it's impossible to discern the value of a variable just by looking at it, even in context. With booleans, though, a logical argument can be made both ways.

There are no sly dilemmas,
no subtleties I see;
Both I encompass gladly,
to be, and not to be.

But in the end, a boolean variable holds nothing more than the result of a condition; true or false.

Answer 2

Since it's been answered well already, just a clarification. The two long words I had in mind were a

boolean variable

which is sometimes called a

truth value

whence the second couplet about disagrement. The one short word, not quite synonymous, would of course be a

bit

Thank you one and all.

Answer 3

My personal guess was a fact, as many disagree on facts, many claim to know the facts, and a fact can't be a maybe.

Answer 4

I thought it would be

(theory of) evolution

Explanation as per request:

I know what is or isn't, but never what might be;

the results at one point of the process of evolution are a given, but only a theoretical all-knowing entity (Laplace's Demon) could accurately predict what evolution will lead to in the future. Added later: forgot my most compelling point here. Evolution itself does not (need to) look forward to function. There is no planning or looking ahead, just basic rules that always apply and will lead to the desired result (in the long term)

And many claim to know me, though many disagree;

This one is fairly straight-forward: many people claim to know (understand) evolution, and claim that it is a fact. However, many people also disagree (often proposing intelligent design instead).

There are no sly dilemmas, no subtleties I see;

Evolution is not about morality, and in a sense is a fairly simple, straight-forward process (though the results that emerge certainly aren't). That's what I thought of when reading "sly dilemmas" and "subtleties".

Both I encompass gladly, to be, and not to be.

Evolution is as much about 'succeeding' as 'failing'. The process of natural selection only works because each entity has strengths and weaknesses, which are only strengths and weaknesses in a given context. What turns out to be strong, will 'be'. What turns out to be overrun by the environment, will 'not be'. Both are necessary for evolution to function.

My explanation may not be perfect but hopefully the idea is clear.