The purpose of fundamental science, the first part of Bolzano’s logic, is to remove all doubt that prevents any use of human reason. This task, he says, has two parts: first, we have to show that there are what he calls truths in themselves, and then, we have to show that humans can know at least some of these truths. Bolzano notes that one might doubt the meaningfulness of both of these tasks, since true skeptics wouldn’t even believe in the existence of other people and wouldn’t then even listen to any of their arguments. Bolzano notes that even if we cannot save such extreme doubters, we can convince people who are in danger of becoming skeptics. Furthermore, he adds, even the most stubborn skeptics live unskeptically and thus have the opportunity to be at least internally convinced, even if they refuse to admit this.
As a preliminary to the first task, Bolzano introduces the notion of proposition in itself (Satz an sich). He does not explain the phrase immediately, but only through comparison with other types of propositions. In other words, Bolzano says that uttered propositions are spoken phrases indicating something that must be either true or false, while a thought proposition is such that is not spoken, but only thought by anyone. Yet, he adds, propositions need not be said or thought at all, and if we ignore the question whether they are or not, we are dealing with propositions in themselves.
Bolzano is at some pains to explain why he can use the German word Satz for the notion he is describing: Satz is etymologically related to the verb Setzen, which implies that there is some person “setting up” this proposition. He explains that the etymology should not be taken literally here, just as a mathematical root of an equation is not at all like a root of a plant. Besides, he states, the concept is needed, and any other possible designation, like judgement (Urteil), would point even more to a thinker behind it. Indeed, Bolzano emphasises again and again that proposition is nothing anyone needs to be thinking (although it can be). This implies, he notes, that propositions in themselves do not exist, although thought of a proposition can exist. Then again, Bolzano points out, propositions in themselves can still concern thoughts (think of a proposition like “I am thinking myself”).
Bolzano is assured that previous logicians have at least implicitly used the concept of proposition in itself: for instance, they have admitted that the order of propositions in syllogisms is irrelevant, which would not be true, if they described the order of thinking and not relations of abstract propositions. True, he admits,they have not spoken of propositions, but judgements, mostly because many of them supposed that the phrase Satz referred only to a subclass of judgements, namely, assertions. Bolzano notes that even the suggested other types, such as questions, can be also seen as assertions: question just is an assertion saying something of the form “I ask this and this”.
Bolzano admits that his description of proposition is no true definition. His excuse is that no proper definition is simply available. The best historical alternative – that it is something that can be true or false – is not a classical definition, according to Bolzano, because it contains a disjunction. Other suggested definitions, he notes, have often concerned thoughts of propositions or then they have assumed the concept to be defined.
Bolzano has introduced the notion of a proposition in itself only to explain the further notion of truth. Words “true” and “truth”, he says, can mean many things, but the most appropriate is that truth is a characteristic of certain propositions in themselves, whether they are asserted or thought or not. Sometimes, Bolzano continues, we speak of truths, when we mean these propositions that have this characteristic. An even further deviation is to speak of true thoughts or judgements that contain true propositions or of collections of propositions or judgements. The least appropriate meaning, Bolzano thinks, is that of speaking of e.g. true friends, where we are referring to an object that truly is what it is described to be.
Just like there are propositions in themselves, Bolzano says, there are truths in themselves or objective truths, that is, truths no matter whether anyone says or thinks it. Just like propositions in themselves, he thinks, truths in themselves do not exist, except when thought by someone. Bolzano does admit that metaphysically speaking, God does know all truths, but this does not lie in the very concept of truth: truth in itself differs from a known truth. Furthermore, he continues, truth differs from certainty, which is a property of judgements, and from existence, although truths can refer to something existent. Interesting is the relation of truth to thinkability and knowability. Bolzano notes that all truths are thinkable, but not everything thinkable is true. Even more, he adds, all truths are knowable and everything knowable is true, but the concepts are still different, because knowledge and thus also knowability have degrees, but truth does not.
Bolzano could not define propositions in themselves, but he suggests we can define truths in themselves. Propositions always have a subject or a topic, of which they figuratively say or predicate something. Propositions are true, Bolzano underlines, if this subject actually has what the proposition predicates of it. The only weak point in this definition, he says, is the word “actually”, which in this context means the same as “truly”. Still, Bolzano thinks, this is no problem, since we can do without this word: proposition is true means that proposition predicates of its subject what the subject has.
Bolzano considers several alternative definitions of truth, dismissing quickly the so-called metaphysical definition, equating truth with existence. A more interesting definition is that of truth as correspondence between thought or representation with its object. Bolzano cannot, of course, accept this definition, because it speaks only of thoughts or representations of truths. Furthermore, he says, no one has really been able to explain what this correspondence is supposed to be. If it is meant to say just that a representation represents its objects, well, Bolzano thinks, this is what representations always do. If it means that representations within a proposition have the same relation to one another as their objects, this cannot be literally true, he points out, because e.g. a representation of God is not the cause of a representation of the world.
Further suggested definitions of truth Bolzano finds even less convincing. Truth cannot be just universal validity, since every person does not know every truth. Furthermore, truth cannot be defined as agreement with the rules of thinking, because these rules are either defined in terms presuming the notion of truth or then the definition also includes probable propositions that are still not true. Finally, truth is not defined by permanence, which is at most a sign of truth, not its essence.
Bolzano criticises attempts to extend the notion of truth. Firstly, he is not fond of the concept of subjective truth or of truth relative to a person, since we already have notions like opinion. Similarly, Bolzano forbids the idea of a formal truth, which at best means something like non-contradictoriness, which should not be confused with truth.
With all these preliminaries taken care of, Bolzano can finally move to his actual task, that is, proving that there are truths in themselves. This does not mean, he underlines again, that we should prove that such truths exist, but only that at least one proposition in itself is true – or to put it in other terms – that the proposition “no proposition is true” is not true. This, Bolzano quickly notes, is evident because “no proposition is true” contradicts itself: if it were true, it would itself not be true. Thus, there must be at least one truth. Even further, Bolzano points out, the same proof can be applied again. Say that we know there to be a certain number n of truths. Well, if we pick out these n truths and consider the proposition “no proposition beside these specific truths is true”, we note again that this proposition contradicts itself and that there are more – and indeed, infinitely more – true propositions.
Bolzano notes that a hardcore skeptic might not be impressed with this proof. They would object that if they are to be convinced by this proof, they must already suppose that they have a capacity to know truth, thus already presupposing that there are truths in themselves. Furthermore, Bolzano continues with the skeptic’s objections, the proof assumes the premiss that “no proposition is true” is a proposition in itself, thus assuming another truth before we showed that there are any truths. Bolzano is not afraid of these objections. Firstly, he admits that the person convinced of the proof must have a capacity to know truths, but they themselves need not explicitly have this as an opinion. Secondly, Bolzano agrees with the skeptic that the mentioned premiss is true and goes even so far as to suggest that its truth is immediately convincing. Yet, he adds at once, this is no problem, but another proof for what we set out to demonstrate. The method Bolzano used was chosen just because it so forcefully showed the self-contradictoriness of all skepticism, but this does not mean that there aren’t other ways to do the same thing.
Ei kommentteja:
Lähetä kommentti