Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!mcsun!ukc!warwick!kingpol!is_s425 From: is_s425@kingston.ac.uk (Hutchison C S) Newsgroups: comp.ai Subject: Re: UNIFIED MODEL FOR KNOWLEDGE REPRESENTATION? (IMPOSSIBLE Message-ID: <1991Jun12.130817.3621@kingston.ac.uk> Date: 12 Jun 91 13:08:17 GMT References: <9106110020.AA17886@lilac.berkeley.edu> <133090@tut.cis.ohio-state.edu> Sender: c.s.hutchison@kingston.ac.uk Organization: Kingston Polytechnic Lines: 103 Nntp-Posting-Host: sappho I am aware of the PAULINE program; also of a program by (I think) Cornelius Wegman which is similar; also of Carbonell's POLITICS. I still believe that 'truth' is an issue. A semantic theory will specify the meanings of well-formed sentences in the language. A semantics built upon a correspondence theory of truth has a commonsensical appeal to it: what, after all, are sentences expressing propositions about if not about the world in which language users live? Conversely, if sentences do not express propositions about the world that can be true or false (referring instead, for example, to speakers' "perceptions" or internal representations of the world), then how can conversants ever know that they are talking about the same thing(s)? A correspondence theory of truth, and a semantics dependent upon it, rescues the theory of semantics from the vagaries of 'mentalism' and 'solipsism' that Stephen Smoliar fears. Let's go back to my four newspaper headlines: Rioting blacks shot dead by police as ANC leaders meet Police shoot 11 dead in Salisbury riot Rebels kill 11 ANC men Racists murder Zimbabweans One might argue (as has one of my correspondents, John Bradshaw) that all four sentences may be true, albeit each expressing only a partial truth. That is, it may be that the predicates 'police', 'rebel', and 'racist' all apply to the agents of the four sentences. That they *may* apply does not, of course, mean that, in a specific case, they *do* apply. Thus I may be happy about the truth of the proposition expressed by the last sentence; others may not be, though be quite happy about the truth of the first and second. Now let's assume that the greater part of what I or anybody else knows is knowledge derived from text (e.g., I know that Bogota is the capital of Columbia because I have read it; I have never been to Columbia to check; perhaps Bogota doesn't even exist). What do readers of each of the four sentences know? 'Know' is a factive verb; does this then fall short of a bona fide sense of knowledge? Does the reader of headline 1 know the same things as the reader of headline 4? If the first and last sentences both express partial truths, why do I find it hard to persuade my fellows that the last headline represents knowledge of the world every bit as much as does the first headline? How is the knowledge that I and my fellow newspaper readers extract from text integrated into what I and they know already? It seems to me that talk of 'partial truths', 'negotiation', and so on, may not get us very far. If I'm negotiating with you, I'm really just trying to tell you why you are (mostly) wrong and I am (mostly) right. If I adduce evidence to support my claims, then we may end up negotiating what counts as evidence. We're stuck in a hopeless regress. (Try telling one billion Christians or one billion Muslims they're wrong -- especially if it is perfectly obvious to you that Humanistic Buddhism is the only right way. Try negotiating with the Jehovah's Witness on your doorstep. Try telling the free market liberal about the unspeakable suffering and brutality that capitalism has wrought upon the cheap labour markets of the Third World.) I mentioned Carbonell's POLITICS program earlier. It is claimed that the program "simulates human ideological understanding of international political events" by "an American newspaper reader" who may be on an occasion either a "US-liberal" or a "US-Conservative". The program actually does no such thing. Carbonell gives, not events, but *reports* of events; the text received by the reader is the content of an utterance act by some speaker who, as much as much as the reader, has "subjective interests, personal motivations, beliefs" (p.2). This being so, it would be naive and indeed counter-intuitive to assume that such interests, motives and beliefs will not have enetered into, first, the speaker's/writer's reasons for uttering the text at all, and secondly, his lexical and themtic choices in the formulation of his utterance. Here is an example form Carbonell (1981): Soviet-backed forces are scoring rapid gains against the Bhutan government. The US is diverting tanks and M-16s, ear-marked for the US army, in an emergency airlift to Bhutan. Carbonell indicates the different responses that the report (or, in his words, "event") would elicit from a "US-liberal" and a "US-Conservative". Clearly other responses would be elicited were the report worded differently. Here are some of my versions: Rebels' advance against government forces prompts US airlift of emergency arms package to Buthan. US pumps arms into Buthan as the Washington-backed regime loses ground to people's army. Buthanese people's gains in struggle to liberate homeland spark panic bid by US imperialists to bolster beleagured puppet dictatorship. Are the reports talking about the same event? If so, the reports are either true or false, and there should be ways of determining the truth value of the propositions expressed. If the reports represent merely the contents of 'perceptions' or 'interpretations', then how can we ever know that we are talking about the same things? (or: how can we be sure that we are talking about the real world at all, and that therefore there is any physical circumstance that can in principle decide the issue?) To get things in context, despite the political flavour that my question may appear to have taken on, my main concern is with automatic knowledge acquisition from text (whatever kind of text it may be). My problem is: is knowledge representation going to be about an intelligent agent's models of the physical world or of speakers' reports about the world? This is a technical rather than a philosophical issue since it impinges directly on what kinds of inference and what sources of knowledge are relevant to the reasoning process. Chris H.