Why not?
The former leaves open the possibility that the “leprechaun” was an illusion or hallucination.
So does the latter. Asserting a statement doesn’t make it absolutely true. At most, taking into account modern sensibilities, the former indicates that the speaker is being self-conscious about epistemology.
It doesn’t make it true, of course, but it says it’s true.
If I started seeing leprechauns, I would indeed get self-conscious about epistemology.
How do you know posting on here isn’t a hallucination?
How would SentientMeat know that anything he sees/hears is not merely a hallucination? Is being able to complicate it to an extreme degree in an internally consistent manner evidence enough that it is not a hallucination? What about his ability to relate multiple interactions qualifies his experiences as anything more than a hallucination? What qualifies ANY experience you ever had as a hallucination?
On to semantics. If you define the experience of seeing a leprechaun as “Seeing a leprechaun”, then how can one argue that they did not see a leprechaun, if “I saw a leprechaun” is how they define the experience they just had?
SentientMeat Your arguments are compelling, and you are one of the most intelligent people I have ever conversed with, however, you tend to lose me on many of the things you talk about simply because I do not have access to the same semantic space that you have. While you have one of the most internally consistent belief systems I have found, how is internal consistency evidence of anything? How do I possibly know that anything you say is anything more than the relation of a very thorough hallucination on your part?
One of the reasons I have believing in anything you say is because you say that everything is physical and that metaphysics and physics do not interact. I disagree that by definition they are mutually exclusive. Physical properties are not the same as physical objects. The meaning of the words I disagree have temporal and spacial properties in and of themselves out of context. “Hard” has no location in time or space. “I am picking up a hard piece of granite on 11.18.05.” described physical properties, but “hardness” in a vacuum without that spacial and temporal context does not exist physically, but it exists metaphysically. Metaphysics doesn’t mean that it doesn’t exist in the physical world, it means that it is not limited by temporal and spacial properties in the same way that “physical” objects are.
Basically to put it succinctly, ‘physical properties’ are not physical out of context. The concept of the rock, and the physicality of the rock are not the same thing.
Erek
Metaphysical semantic framework a.k.a. worldview. ‘Hallucinations’ behave differently than ‘real things’.
I don’t. I can only strongly believe that the solipsistic position is false.
It is enough to make me believe so, but not enough to give me absolute certainty.
If the versions of other witnesses (either other people or experimental apparatus such as a camera) are at odds with mine, I might well re-assess my version as being a hallucination, rather like I might assess a digital photograph as being genuine or Photoshopped.
They must take all the relevant facts into consideration, such as camera footage, diagnoses of temporary anatomical conditions, and the logical consequences of “what they saw”.
In and of itself, it isn’t. I can only place shapes on your monitor which are the semantically coded output of my brain, with all its emotions and logical processing and whatnot. If you disagree (ie. output some other position than mine), I can ultimately only repeat myself.
You don’t, any more than you know I (or, indeed, you) “really exist”.
I do not simply say that: it is a logical consequence of their mutually exclusive definition.
Meta: beyond or transcending.
Agreed: a physical object is a spatial arrangement. A physical process (like consciousness) is a temporal arrangement.
It is the label a human sensor bestows upon an object which has undergone a physical process of eg. being cut with a diamond at a given rate. All of this is still, ultimately, physical by nature.
A linguistic referent which does not refer to any real thing is not necessarily metaphysical, just rather useless. For example, a random string of symbols ‘grythu’ is a “word in a vacuum”. Again, that does not make it unphysical.
Arrangements (eg. of symbols or phonemes, ie. “words”) sometimes seem to violate spatio-temporal boundaries (ie. “physical laws”) but actually do not. For example, sweeping a laser spot across the moon seems to make the spot go faster then light, violating the physical laws of relativity. But no object is travelling so fast: it is just an arrangement in time of photons, just like eg. a line of dominoes a million miles long could all fall at once.
Yet, I consider that the “concept” is effectively an average of all the memories of rocks you have ever seen. And memories, as I directed you earlier, are physical things. That is, “concepts” are as physical as memories, which are as physical as the things themselves.
“Hardness” in a vacuum does not exist metaphysically. In a vacuum, “hardness” does not exist at all.
“Hard” only has meaning within a spatial and temporal context, i.e., within a concept of physicality, explicit or implicit. Otherwise, it’s like saying that chocolate is irrelevant to the meaning of “chocolate flavored".
I can’t speak for Sentient, but I think his view is that while the “physical properties” of the rock describe and define the rock, they’re not in the rock per se; rather, “physical properties of the rock” are concepts that exist as spatio-temporal arrangement of our physical neurons. Hence, “the rock” and “the concept of the rock” are indeed not the same thing, but they’re both physical.
other-wise, if your 246 posts to date since August 1999 are all that precise and concise, I really will have to look them all up some time. Truly, you must be the uber-lurker of the SDMB. 
“Can someone prove to me that consciousness exists?”
Being simple minded, can I ask would the concept of proof have any meaning in a context which conciousness did not? However one would define the terms, “proof” would imply “conciousness” in all cases where any reasonable consistency of usage maintains. No?
“His was a great sin who first invented consciousness.”
from The Diamond As Big As The Ritz - F. Scott Fitzgerald.
I think the OP’s question at bottom is about what is or is not real. That’s one of the topics that the first, pre-Socratic philosophers tackled and they didn’t have an answer either.
That’s the fascinating thing about the subject of philosophy. In it there are no settled questions.
Have you heard of CEMI field theory? That theory is that consciousness is an electromagnetic field that plays a role in coordinating the activation potentials of our neurons, leading to consciousness and free will. Essentially when unconscious behavior leads to a crossroad in behavior consciousness is activated to pick a pathway. Johnjoe McFadden writes pretty heavily on the subject.
Pro:
http://www.surrey.ac.uk/qe/pdfs/mcfadden_JCS2002b.pdf
http://www.mindcontrolforums.com/news/electromagnetic-field-theory-of-consciousness.htm (the weblink for that article sucks, I couldn’t find one w/o mindcontrolforums in the title)
Anti:
http://www.phy.auckland.ac.nz/assets/pdf/difficulties_jcs.pdf
Study of consciousness in general can be found at the Journal of Consciousness