نشریه منطق پژوهی
سال پنجم شماره 2 (پاییز و زمستان 1393)

external world and in the mind as well) paradox، so many solutions have been suggested: The difference in the intension and extension and its equivalent; the difference in the battī and lā–battī and its equivalent; and so forth. Having a glance at the incorrectness of these resolutions، the essay shows the knowability of the absolute non–existent. Although here a few of thinkers previously have tried to show the knowability، we will show that their resolutions، due to not paying attention to the exact and strong definition of the unknowable and un-declarable absolute non–existent، are problematic. By summing up the different versions of the meaning in question، we will argue for the knowability of the absolute non–existent by means of four proofs: 1. the principle of non–contradiction; 2. non–existence qua non–existence; 3. the non–existentiality of the subject; 4. proof by reductio ad absurdum.

According to a rule in Avicenna's logic, there exists cohesion between any two necessary hypothetic propositions with identical quantity, different quality, identical antecedent, and denial of the consequent. The rule is introduced and has been argued for, by Avecinna. After him, this rule is criticized by Avicennian logicians. Khunaji questioned Avecinna’s pre-assumptions of this proof by examples of natural language. After Khunaji, some logicians like Nasir al-Din Tusi, Qutb al-Din al-Razi, and Qutb al-Din al-Shirazi tried to answer Khunaji’s critiques by presenting some better formalizations of Avecinna’s arguments or defending his pre-assumptions. In this paper, after introducing the arguments of both sides together with their detailed formalizations, it is concluded that the answers to Khunaji’s critiques are not enough to prove the aforementioned rule, and accepting this rule still requires new arguments.

A fortiori logic is a kind of formal logic which its arguments, unlike the common arguments of Aristotelian logic, has four terms through which after comparing usually two persons, things, works to each other, the description of one of them is ascribed/ denied to/ from the other. This logic, in spite of Sion’s belief, is found in Quran, so richly that we can say that it is the prominent logic of Quran. In this research, I will study a fortiori logic in Quran, after giving an introductory explanation of it.

Shams al-Din Samarqandi, a seventh Iranian logician, has proposed a new theory on conditional syllogism against Avicenna. Avicenna believed that conditional syllogism had only 19 valid moods; but Samarqandi, denying this similarity, validated only 7 moods. Samarqandi considered in his analysis only the quality conditions of the syllogism and did not pay attention to quantity conditions and in providing counterexamples for the invalid moods, he ignored their quantificational differences. If we consider just quality, as Samarqandi did, we’ll find a surprising similarity between his valid moods and the contemporary relevance logic, so that all Samarqandi’s valid moods are valid in relevance logic and vice versa. But if we look at the quantity of the propositions involved, we’ll encounter some difficulties, which are rooted in his interpretation of conditional quantifiers.

Semantic stipulations, i.e. the principles which are the main constructors of the meanings of words, have different forms for each category of words. Kripke`s theory is the most suitable model which identifies the appearance of the stipulations. In general, semantic stipulations are some usages of a word that has been accentuated. So, as long as the stipulations remains fixed, discoveries and inventions do not change the meaning of a word. Also, to justify the way which any meaning engender from semantic stipulations and how the meanings of the words in one sentence affect each other, radial model is very suitable one. Radial model, unlike those models which concentrate on the conceptual and obstruct definitions of words, shows a dynamic way of producing meanings.

In traditional Aristotelian logic, the absence of a logical relation between ‘is’ and ‘ought’ statements seems to be evident, due to some characteristics of the logic. Prior relying on this fact that modern logic does not possess such characteristics, present a paradox against the advocates of the logical gap between ‘is’ and ‘ought’. In this paper, we, first, explain this paradox and a number of philosophical solutions have been proposed to solve it. Then, we illustrate and evaluate the Beall’s ‘many-valued logic’, which has been introduced as a solution to this paradox. We’ll see that this paradox could be solved in the context of the ‘relevant logic’ too. But besides of this paradox, Prior presents two other arguments, which although these two logics solve the paradox, we’ll show that each of them is unable to response to these two other arguments.