ابرازگرایی منطقی، راه‌حلی برای دفاع از موصل بودن استدلال‌های منطقی

نوع مقاله : علمی-پژوهشی


استادیار گروه فلسفه دانشگاه اصفهان، اصفهان، ایران.



لوئیس کرول در مقاله 1895 خود به نام "لاکپشت به آشیل چه گفت" معمای سختی را دربرابر منطقدانان قرار داد: آیا استنتاج نتیجه از مقدمات یک استدلال معتبر قیاسی مستلزم تسلسل است؟ در این مقاله با بکارگیری روش تحلیلی-استنباطی، نشان می­دهیم راه نجات از این تسلسل این است که قواعد منطقی را همچون استعدادهایی بدانیم که ما را در حرکت منطقی در استدلال راهنمایی می­کنند. قواعد منطقی، باورهایی در ذهن نیستند که بازنما و توصیفگر حقیقتی عینی باشند. برای صورت­بندی این دیدگاه، با کمک از نظریه غیرشناختی بودن احکام اخلاقی در فلسفه اخلاق، منطق را مجموعه­ای از آموزه­های غیرشناختی معرفی می­کنیم که دستورالعمل هر استنتاجی است. همچنین با دفاع از اینترنالیسم منطقی نشان می­دهیم که منطق به تنهایی برای حرکت ذهنی در طول استدلال کافی است و لازم نیست باورهای دیگری را در قالب گزاره به مقدمات استدلال اضافه کنیم تا اخذ نتیجه ممکن شود.  ابرازگرایی منطقی دیدگاه ضدرئالیستی در معرفت­شناسی منطق محسوب می­شود و منطق را پیشفرض هرگونه فعالیت عقلانی می­داند.


عنوان مقاله [English]

Logical expressivism as a defense for the necessity of entailment of logical arguments

نویسنده [English]

  • Hooman Mohammad Ghorbanian
Assistant Professor of Philosophy, University of Isfahan, Isfahan, Iran.
چکیده [English]

In his famous 1985 article “What the Tortoise Said to Achilles”, Lewis Carroll offers a regress that suggests we could never reach the conclusion of a deductive argument. In that story, logical rules are conditional propositions that adding them to an argument never provides enough reason to infer the conclusion. For example, when we are to use modus ponens, “if (if P then Q) and (P) then (Q)”, the rule itself does not justify us in a way that we could follow (Q) from (if P then Q) and (P) as the premises. 
Here, we follow a path that in Ethics is called non-cognitive moral expressivism. According to logical expressivism, logical inferences are not just mental states without any consequences, but we should consider logical facts and rules of logic as some dispositions that create capabilities for making inferences from premises. 
Methods and Material
The method of research here is based on content analysis and logical inference. First, the main problem is established, and then I tried to apply the solution introduced in Ethics for the same problem in Logic. In the end, I concluded that disposition could serve as a good reason to reach the conclusion in arguments.
Results and Discussion
It seems as if we should have a principle that makes whoever faces an argument draw the conclusion. In the philosophy of Ethics, these principles are usually expressed by “ought”, so in logic, we should express inferential rules, such as MP, as follow:
- Everyone that believes P and if P then Q ought to believes Q too.
The normativity of logical rules is defended by some famous philosophers such as Wittgenstein and Ryle. Wittgenstein believes rules of inference cannot be true or false, since they are just like instructions or commands that we must follow like instructions in a handbook. What I added here is that these instructions themselves could make the mind move in a certain direction without any need for other reasons. Ryle believes that logical rules are not some sort of knowledge of facts, but actually, are “how-to-act” or knowledge of performance; in other words, we should explore the issue at hand in practical wisdom rather than theoretical wisdom. When we know a logical rule, we know how to act in a certain way, not that this knowledge is an extra premise that should be added to the argument.
Boghossian suggests this idea that passing through one piece of information to another one does not need further belief to justify this move. Logical dispositions, when we try to have a valid inference, make the logical move from premises to the conclusion possible. As Wittgenstein put forward in his Philosophical Investigations, acting according to logic is like following some rules, and our knowledge about these rules is dispositional: “When I obey a rule, I do not choose. I obey the rule blindly”. In this way, logic is internally sufficient and justified. Logical internalism explains this idea as follow:
- Beliefs, in their propositional form, do not motivate to act.
- Logical rules motivate to act according to them.
- Therefore, logical rules are not beliefs in propositional form.
The conclusion introduces a simple form of logical non-cognitivism that suggests knowledge of logic is not knowledge about facts, but rather logic contains norms that lead agents to infer properly.
As the result, the solution for Carroll`s puzzle suggested here is that we should consider logical principles as dispositions that guide us in our mental movements; logical principles, in this way, are not some sort of beliefs that represents facts. In articulating this solution, we use a theory in the philosophy of ethics that considers moral judgments as non-cognitive mental states. In logical non-cognitivism, logic is a handbook for deducing. Also, according to logical internalism, non-propositional rules of logic are enough to entail the conclusion and there is no need to add other premises to the argument. Logical expressivism is an approach in the epistemology of logic that regards logic as a self-sufficient knowledge and as a prerequisite for any rational activity.
Basic principles and rules of logic should not be presented as descriptive propositions. The justification of inferential rules is based on their normativity. All our knowledge is not objective and descriptive, but some part of it is normative and how-to-do norms. It is clear that this picture of logic is not realistic and logical expressivism should be considered an antirealist theory and must be interpreted in this way: logic is not trying to paint a picture of the word, rather it is the precondition for any objective knowledge about the world.

کلیدواژه‌ها [English]

  • Lewis Carroll
  • cognitive states
  • logical non-cognitivism
  • logical internalism
  • logical expressivism