Theism vs. Atheism debate

 I believe he is making a deeper philosophical distinction.

And you may be right.  What I'm trying to do is pin down what 'X exists' means. 

If you don't lke the sun as an example, consider Neptune which was discovered in 1846.  Did it exist in 1845?   I have no problem saying it did.

If someone who lived in 1845 claimed (in 1845) that Neptune (even by some other name) "exists" without evidence, their claim would rightly be dismissed.  That specious claim would not be supported by the evidence currently available at that moment in time.

someone who lived in 1845 claimed (in 1845) that Neptune (even by some other name) "exists" without evidence, their claim would rightly be dismissed.  That specious claim would not be supported by the evidence currently available at that moment in time.

I see that as over-complication.   The question asked is whether neptune existed in 1845, purely for the purpose of clarifying the intuitive meaning of 'exist'.  I think the ordinary, plain meaning of exist is such that the answer is a simple 'yes'.

Agreed, there are issues about our 'knowledge concerning the existence of neptune',  but the question asked was not 'did we know Neptune existed in 1845?'  - the question was whether it existed in 1845.

Neptune did not change between 1845 and 1846 - what changed was us; we learned that neptune existed - in other words, the existence of neptune did not change, it was our knowledge its existence that changed.  

If i say 'neptune existed in 1845' I am saying something about the 'existential state' of that planet at that time.   I an not saying anything about our knowlegde of that state at that time.  If I wanted to say something about our knowlege then I wouldn't say 'neptune came intoexistence in 1846' - that sentence gives a completely incorrect picture of a planet popping into existence at that time.

The question asked is whether neptune existed in 1845, purely for the purpose of clarifying the intuitive meaning of 'exist'.

I believe the meaning of "exist" should only include what is either (currently) scientifically verifiable (OR) logically necessary.

Exclusive, private, gnostic, personal Qualia, like consciousness, and other hypothetical things or experiences do not properly "exist" (unless and or until they can somehow be rigorously defined and Quantified, perhaps by brain-scans or some other method).

Why do pieces necessitate a whole? And what are these pieces that can be objectively delineated?

The pieces are what you know.  Do you know "everything"?  If not, then you can logically deduce that you know "part of" "everything".

This seems weird to me. Is, in your opinion, knowledge part of "everything"? (Then You get into the whole how do I know that I know that I know that I know...)

Is knowledge certainly true? or is it just probable? If it is not certainly true, how could we say that knowledge is part of reality? 

I either think I know everything or don't know anything, personally if knowledge is certainly true. If knowledge is just probabilistic, I have no idea what I know. 

I think I am confused about what you mean by something and nothing again. But maybe we should revisit existence itself: I tend to go by: A thing is said to exist if change in the universe can be traced back to it. 

I believe in epistemological limits.  Something can be said to "exist" if it is scientifically verifiable and or a logical necessity.

the scientifically verifiable part of this I believe is equivalent to what I said.

My question then to you is "does logic exist." That is, is logic a logical necessity or is it scientifically verifiable.

I believe this gets circular since science uses a particular logical system (or rather, particular logical systems since it changes depending on domain). And saying logic is logically necessary is clearly circular.

My point here I guess is that the logical system used has little justification and even by using the classical Aristotlean logical system like non-contradiction etc. you get weird stuff in physics likes Schrodinger's cat etc. that seem to say, hey, you need a different system. 

Your "imaginary friend" example is a little too generous for my taste.

I'd say that the "imaginary friend" may possibly "exist" beyond my epistemological limits, but since it is neither scientifically verifiable nor a logical necessity, it would not qualify as "real" or "actual" or "existent" in any practical or factual sense.

Let's use then an imaginary force (same idea, but a little more down to earth). Imagine all humans always lived their lives on planet x, which although having about the same mass as earth, spins about 17 times faster (ignoring all the practical issues of living on such a planet). They may well come up with a fundamental force that repels (let's say for good measure every object in the universe spun like this). This is a "fictitious" force in physics, in the same way as centripetal force is a fictitious force. My point is, the force is scientifically verifiable. Just like centripetal force is. And so would be the child's imaginary friend with a good definition of imaginary friend. 

If I wanted to say something about our knowlege then I wouldn't say 'neptune came intoexistence in 1846' - that sentence gives a completely incorrect picture of a planet popping into existence at that time.

Someone in 1845 could say, factually, "there are only seven planets in our solar system".

Someone in 1845 could say, factually, "there are only seven planets in our solar system".

If it is a fact that only 7 planets existed in 1845, how could an 8th one be discovered?  It must have existed all along, waiting to be discovered.

I wouldsay the existence of Neptune is independent of our knowledge about it.  What the someone in 1845 should have saidis 'there are only 7 known planets' - that is factually true.   That there are only 7 is factually incorrect, albeit the error is not known.

My view is 'there is no god' is a 'scientfic fact', not a 'mathematical fact', meaning that its not proven or provable by abstract logic but there is evidence [?] against the existence ofgod, and nothing that forces rejection of it [rejection of the unspecified evidence against (a deistic) god?].

And, keithprosser, something is said to exist if a change in the universe is traceable back to that thing. 

A person with 10 heads. I can't show you something that doesn't exist of course, but we can imagine something that doesn't physically exist, if you just take everything to exist, it's a pretty useless term

Previously you wrote

something is said to exist if a change in the universe is traceable back to that thing. 

Dekaheads do not exist because there is no effect in the universe traceable back to them.

In my formulation, dekaheads have no traceable effect because they do not exist.

But what is your definition of existence?

False knowledge does not exist.

Exist means to occur, either physically or metaphysically.

A person with 10 heads. I can't show you something that doesn't exist of course, but we can imagine something that doesn't physically exist, if you just take everything to exist, it's a pretty useless term

Your invocation of "a person with 10 heads" has caused me to write this response.  Do you believe this qualifies as "a change in the universe is traceable back to that thing [the 10 headed person]"?  Do you believe "a person with 10 heads" now exists simply because your description of it has caused some detectable thing to happen?

I'd say the defintition of knowlege as 'justified true belief' is so widely used you need a very good reason to define 'knowlegde' as anthing else, and if you do it has to be made very clear. 

If you tacitly drop the requirement that an item of knowlege is true then chances are a lot of talking at cross-puposes will ensue!

We could extend the meaning of 'X exists' so that it includes 'thoughts about X exist' , but I think that is asking for confusion and misunderstanding/  I much prefer a narrow sense of exist,albeit it means having to be a it pedantic about what it is that exists.