Let's begin with some more logic.
(( P entails Q) AND NOT-Q) entails/logically implies NOT-P
That is te logic the skeptic uses to show that he is right. To prove that this is a valid reasoning we create a so called truth-table. Looks like this.
((p --> q) & ~q) --> ~p
..1..1.. 1. 0. 01.. 1.. 01
..1..0.. 0. 0. 10.. 1.. 01
..1..1.. 1. 0. 01.. 1.. 10
..1..1.. 0. 1. 10.. 1.. 10
.....(3) ...(4) (1). (5). (2)
Step (5) is the final evaluation. It says: whatever truth-value p and q have, you will always get to the same conclusion. That is what those four 1-s mean.
This is the well known 'modus tollendo tollens' law of logic.
Information from Wikipedia -------------------------- quote
Modus tollens became well known when it was used by Karl Popper in his proposed response to the problem of induction, falsificationism.
However, here the use of modus tollens is much more controversial, as "truth" or "falsity" are inappropriate concepts to apply to theories (which are generally approximations to reality) and experimental findings (whose interpretation is often contingent on other theories). Thus (to take a historical example)
If special relativity is true, then the mass of the electron has a specific dependence on velocity.
Experimentally, the mass of the electron does not have this dependence (Kaufmann (1906)).
Therefore, special relativity is false.
Einstein rejected this argument on the grounds that the alternative theories that appeared to be validated by the experiment were inherently less plausible than his own. -- END QUOTE
I give you this quote because it is so interesting and gives rise to many philosophical considerations. But not now....let's stick to the skeptic and the possibility to find a refutation.
Ok ....this was the original deduction:
If I know that I sit at my computer, then I know that I am not a brain in a vat.
I do not know that I am not a brain in a vat. So,
I do not know that I sit at my computer.
What we have to do is to show that "I do not know that I am not a brain in a vat" makes no sense, or even that the whole argument makes no sense
St. Augustine's "Contra Academicos" (354 – 430) was the last major attempt before the Renaissance to come to grips with skeptical questions in epistemology (theory of knowledge).
Augustine was strongly attracted by Cicero's views and the Platonism of the Middle Academy. Part of the resolution of his personal religious crisis was his realization, presented in"Contra Academicos" and earlier writings, that skepticism can be completely overcome only by revelation.
From this standpoint philosophy becomes faith seeking understanding and I assume that not everyone of you will be satisfied with this conclusion. At least I, myself, dont think that this standpoint is very convincing. Yet this conclusion held till Descartes.
The Cogito of Descartes (died 1650) seemed a refutation of skepticisme. We CAN know something for certain, namely, "I think, so I am." Of course skepticism was refashioned and redirected to show that Descartes had found nothing certain at all.
Without hesitation you may call David Hume (died 1776) as the creator of our modern skepticism. When we examine what we believe and what leads us to believe it, we find that "Philosophy would render us entirely Pyrrhonian, were not Nature too strong for it." , as Hume said.
The skeptical problems notwithstanding, we are naturally constrained to believe all sorts of things. according to Hume. Under normal conditions we find that we are led by nature to believe that the future course of events will resemble the past course, and on this we base our so-called "reasonable" or "scientific" views and expectations about the world.
But nature does not refute complete skepticism. It only prevents us from believing in, or accepting, the doubts that result from skeptical reasonings.
In 1764 Thomas Reid, also a Scottish philosopher concludes that when the conclusions of philosophy run counter to common sense then there must be something wrong with philosophy.
Nobody can believe and act by complete skepticism, he claimed, and as a solution he formulated his comon sense realism. Nowadays this approach to face skepticism is called Philosophicla realism.
That is also the origine of our own brain in the vat, an idea formulated by Hilary Putnam in 1981. The funny thing is that Putnam has clarified that his real target in this argument was never skepticism, but philosophical realism.
Philosophical realism is the view that the categories and structures of the external world are both causally and ontologically independent of the conceptualizations of the human mind.
Later Putnam adopted a rather different view, which he called "internal realism". Internal realism is the view that, although the world may be causally independent of the human mind,
the structure of the world—its division into kinds, individuals and categories—is a function of the human mind, and hence the world is not ontologically independent.
So the premis "I do not know that I am not a brain in a vat." is false, when we adhere this philosophical realism and begin the debate about what it means when I say "I KNOW P.
Our skeptic argument depends on the assumption that the external world is mind-independent and that it is logically possible for sense experience to represent there to be a physical world of a certain character even though there is no physical world, or at least no physical world of that character.
We can deny that assumption of independence. We can maintain that facts about physical objects hold simply in virtue of the holding of the right facts about sense experience.
Any world in which the facts of sense experience are as they actually are is a world in which there is an external reality of roughly the sort people take there to be. In fact the later view of Putnam.
We could choose another strategy and claim that the whole skeptic argument is in fact an empty shell. Is it a hypothesis: is my brain in a vat or not? Get real, who cares? Whether the hypothesis is true or false....it makes no difference at all.
I keep experiencing the same reality, having the same sensory experiences, so what is the big deal with this skepticism? Well...there is one weak point in this view. It still is logically possible that one day some creature comes by and show me that I am a brain in a vat.
You also could say...OK this skeptical argument holds and makes sense, but only in a context where you demand extremly high epistemological standards, for instance in a philosophical debate.
But in the normal daily context, or in a context of practical scientific research this argument has no meaning at all.
Now what should we conclude? Have we found a definite refutation of skepticism? I dont think so and I wonder if it is necessary.
The fundamental claim of skepticism is, that we should be aware of the impossibility of THE FINAL ANSWER. Everytime a philosopher shows up, claiming he or she has the final answer (think of people like Dawkins, Rand, Marx and so on) the skeptic will raise his hand and ask a question.
Skepticism is not a philosophy like materialism, idealism or empiricism, it is a basic philosophical attitude like history shows. And here we might conclude with the observation that skepticism is a part of our nature, which keeps us open minded.
[13:36] Samuel Okelly: hello every1 :) apologies for being late
[13:36] Gemma Cleanslate: :-)
[13:36] Ze Novikov: smiles
[13:37] herman Bergson: Well for now this wil be my last word on skepticism....but we will run into it time and again I am afraid
[13:37] itsme Frederix: why afraid?
[13:38] herman Bergson: not literally Itsme..of course...
[13:38] herman Bergson: In fact ..I love it ^_^
[13:38] itsme Frederix: sorry was close reading
[13:38] Gemma Cleanslate: lol
[13:38] herman Bergson: Most interesting is that we cant escape this kind of reasoning
[13:39] Aby Karsin: Do you think that skepticism always leads to a dead end (no knowledge so no action perhaps)?
[13:39] itsme Frederix: More interesting is that we might get a use out of it, just sharpening our reasoning and thoughts
[13:39] herman Bergson: No Aby..that is not the meaning of skepticism
[13:39] Alarice Beaumont: no.. skepticism helps to proof and motivate peopel to go on looking
[13:39] herman Bergson: It is not denying knowledge at all
[13:40] herman Bergson: It questions the justification of knowledge
[13:40] Cailleach Shan: One who instinctively or habitually doubts, questions, or disagrees with assertions or generally accepted conclusions.
[13:40] Aby Karsin: insn' skepticism saying that we can't have a complete knowledge?
[13:40] Cailleach Shan: This is my dictionary definition....
[13:41] Alarice Beaumont: well.. i don't think scepticism is negativ...
[13:41] herman Bergson: I dont know what you mean by complete knowledge, Aby, but absolute certainty...yes that is questionable for the skeptic
[13:41] Alarice Beaumont: one need natural scepticism to explore things
[13:41] Ze Novikov: indeed
[13:41] Rodney Handrick: agreed
[13:42] herman Bergson: Yes....that is why Skepticism through history never was a philosophpy
[13:42] Aby Karsin: i was aiming to Montaigne when I said that
[13:42] itsme Frederix: mmm Herman told us already skeptism is natural, and now we create a degree natural natural
[13:42] herman Bergson: As I said in another lecture...
[13:42] Alarice Beaumont: accepting everything like it is would be a step backwards
[13:43] herman Bergson: to some extend philosophy has been the continuing fight against skepticism through the ages
[13:43] Ze Novikov: yes
[13:43] herman Bergson: I think that the real target of the skeptic is dogmatism
[13:43] itsme Frederix: philosophy no doubt makes a claim it can not prove but which is in my opinion valuabl
[13:44] herman Bergson: Yes Itsme ..I agree..skepticism doesnt upset me at all..^_^
[13:44] itsme Frederix: what about sofists
[13:45] herman Bergson: hmmm....we should re-read Plato's dialogs on that issue Itme
[13:45] Samuel Okelly: i see skepticism as highlighting the limitations, in an epistemological sense, of what it means "to know"
[13:45] herman Bergson: Oh yes Samuel....absolutely
[13:46] Ze Novikov: bingo !!
[13:46] itsme Frederix: but, there is always a but, we should not loose our ground by highlighting
[13:46] herman Bergson: So look forward to question 19...^_^
[13:47] herman Bergson: Just a little deviating from the subject....
[13:47] herman Bergson: When I saw this modus tollendo tollens I thought...where did that come from
[13:47] herman Bergson: who invented it....
[13:47] herman Bergson: why should I accept it....
[13:48] herman Bergson: and then you dig into the history of logic......amazing
[13:48] herman Bergson: Aristotle never thought of this way of reasioning
[13:48] herman Bergson: he never wrote about the :if ....then " relation in logic
[13:49] herman Bergson: It took 300 years....Philo of Alexandrai...who did
[13:50] herman Bergson: and in the Middle Ages it was al,most ignored too, because they focused on Aristotelian syllogisms
[13:50] herman Bergson: With the rise of science....hypothetical reasoning..........mankind was willing to accept this way of deduction...
[13:51] herman Bergson: and then we have reached 1590 or so Francis Bacon and all after him
[13:51] herman Bergson: And now this way of reasoning is the core of our logic...amazing
[13:51] herman Bergson: But this just as a side track ^_^
[13:53] itsme Frederix: On the other way, in math the prove using a statement and proving it would lead to a contradiction was used in early days (euclidian)
[13:53] herman Bergson: Cailleach ..you show typing but it never shows???
[13:53] Cailleach Shan: So Herman, if I really am just a 'brain in a jar' then everything is just the way it is and all I have to do is just sit and watch the play. I quite like that idea.
[13:53] herman Bergson: chat lag...
[13:53] Gemma Cleanslate: well i do not
[13:54] Gemma Cleanslate: i think she is caught in the type
[13:54] herman Bergson: Yes. Itsme..the Stoics knew of this kind of reasoning too...but the syllogistic logic of aristotle was dominant for ages
[13:54] Gemma Cleanslate: that happens
[13:54] itsme Frederix: just for the record, we are all a brain in the jar/skul as long as we think we are just brain
[13:55] herman Bergson: Yes Cailleach...life is like in the Matrix..^_^
[13:55] herman Bergson: Another remark for the future...
[13:55] herman Bergson: that quote from Wiki
[13:56] herman Bergson: Were Einstein didnt accept the Popperian falsifiacation because his theory was more plausible...
[13:56] herman Bergson: That is a very interesting observation...
[13:56] itsme Frederix: in a way these logic lectures make us speakless, and herman sparkling
[13:56] herman Bergson: I guess it wil show up when we discuss the possibility of knowledge
[13:57] herman Bergson: Itsme...plz ^_^
[13:57] Cailleach Shan: lol.... that's very logical Itsme
[13:57] Gemma Cleanslate: :-)
[13:57] herman Bergson: Ok...call me Spock from now on
[13:57] Ze Novikov: lol
[13:57] itsme Frederix: meant to be a good gesture
[13:57] Ze Novikov: where are the ears?
[13:57] Samuel Okelly: when it is asked "... Get real, who cares? " arent we being asked to give up on searching for "truth"? because in order for us to "get real" we surely need to establish what "real" actually is
[13:57] herman Bergson: I appreciate that Itsme ...:-)
[13:57] Cailleach Shan: Prof. Spok
[13:58] herman Bergson: You may choose....
[13:58] herman Bergson: we have the Startrek Spock and the educator Dr. Spock of RL
[13:58] itsme Frederix: Sartre
[13:58] bergfrau Apfelbaum: herman and class! : -) thanks for the interesting hour! unfortunately I must now go :-((( need still another gift. it is logical that I come too late if I do not go now
[13:59] Ze Novikov: :))
[13:59] herman Bergson: It is Bergy...:-)
[13:59] itsme Frederix: Berg you might gain from relativism and speed of light
[13:59] bergfrau Apfelbaum: :-) sry"" see u on tuesday
[14:00] herman Bergson: Ok..:-)
[14:00] itsme Frederix: Nice lecture Herman, give us some tools and training in reasoning
[14:00] herman Bergson: Well...I have stirred your jars / vats enough I think...:-)
[14:00] Gemma Cleanslate: might be good
[14:00] Ze Novikov: again thxs herman very much...see you all next week if not sooner..
[14:01] itsme Frederix: its mostly java what you find in a jar
[14:01] Gemma Cleanslate: I will be away next week and will miss 2 classes
[14:01] herman Bergson: No..LSL script Itme..:-)
[14:01] Cailleach Shan: Me and my jar will time travel back to my RL reality now..... cu everyone and thanks.
[14:01] Samuel Okelly: thanks again herman :) cheerio for now every1 :)
[14:01] herman Bergson: Oh dear Gemma.....take care and be strong :-)
[14:02] Gemma Cleanslate: yes thank you :-)
[14:02] herman Bergson: Bye Samuel
[14:02] Gemma Cleanslate: Bye
[14:02] Gemma Cleanslate: all
[14:02] Rodney Handrick: bye
[14:02] Alarice Beaumont: this was a lot today again :-)
[14:02] itsme Frederix: Good lecture good class thx all I was able to participate
[14:02] Socratle Kiranov: bye (en bedankt)
[14:02] Alarice Beaumont: bye everyone :-))
[14:02] itsme Frederix: Socrate that is niet grieks
[14:02] Socratle Kiranov: nope :)
[14:03] Socratle Kiranov: sorry
[14:03] Yakuzza Lethecus: thx
[14:03] Yakuzza Lethecus: cya all!