# A problem with Modal Logic (necessary truths)

## Is modal logic true?

Standard non-modal logic shows us how to understand logical words such as ‘not’, ‘and’ and ‘or’, which are truth-functional. The modal concepts are not truth-functional: knowing that p is true (and what ‘necessarily’ means) does not automatically enable one to determine whether ‘Necessarily p’ is true.

## Are logical truths necessary?

In his conclusion, Quine rejects that logical truths are necessary truths. Instead he posits that the truth-value of any statement can be changed, including logical truths, given a re-evaluation of the truth-values of every other statement in one’s complete theory.

## What’s the point of modal logic?

A modal is an expression (like ‘necessarily’ or ‘possibly’) that is used to qualify the truth of a judgement. Modal logic is, strictly speaking, the study of the deductive behavior of the expressions ‘it is necessary that’ and ‘it is possible that’.

## What is modal logic with example?

Even in modal logic, one may wish to restrict the range of possible worlds which are relevant in determining whether ◻A is true at a given world. For example, I might say that it is necessary for me to pay my bills, even though I know full well that there is a possible world where I fail to pay them.

## What is possibility and necessity?

Possibility and necessity are related. Something is possible if its failing to occur is not necessary; if something is necessary, its failure to occur is not possible. Divers (2002), 3-4, provides a nice summary: “Possibility rules out impossibility and requires (exclusively) contingency or necessity.

## What is alethic truth?

Alethic truth, Bhaskar (1994) tells us, is. a species of ontological truth constituting and following on the truth of, or real reason(s) for, or dialectical ground of, things, as distinct from. propositions, possible in virtue of the ontological stratification of the.

## What is logically necessary mean?

When something is logically necessary, it is true by definition. These can also be called analytic truths. If we can prove that something is true because “it could not be otherwise,” then it is logically necessary. The statement is true with an absolute degree of certainty.

## Are arguments based on faulty reasoning?

Logical fallacies are arguments that may sound convincing, but are based on faulty logic and are therefore invalid. They may result from innocent errors in reasoning, or be used deliberately to mislead others.

## What is the relationship between logic and truth?

Logic uses the concept of TRUTH, but a very simplified one. See Tarski’s Truth Definitions. But in order to use it, logic does not need a philosophical account of TRUTH. Logic chases truth up the tree of grammar — see Quine, academiaanalitica.files.wordpress.com/2016/10/…

## What is a modal argument in philosophy?

Modal arguments are generally arguments that depend on claims about possibility, necessity, and impossibility, different “modes” of truth or existence. To say that “1+1=2” is necessarily true, or to say that a square circle can’t exist, is to make a modal claim.

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## What are the types of modal logic?

Modal logics in philosophy

• Alethic logic.
• Epistemic logic.
• Temporal logic.
• Deontic logic.
• Doxastic logic.

## Is modal logic first order?

First-order modal logics are modal logics in which the underlying propositional logic is replaced by a first-order predicate logic. They pose some of the most difficult mathematical challenges.

## Do possible worlds exist?

Possible worlds exist – they are just as real as our world; Possible worlds are the same sort of things as our world – they differ in content, not in kind; Possible worlds cannot be reduced to something more basic – they are irreducible entities in their own right. Actuality is indexical.

## What does a diamond mean in logic?

Modal Logic deals with the modal notions of possibility and. necessity. We will have two new logical operators: the box (□) and. the diamond (♦), which will mean necessity and possibility. respectively.

## What is a modal system?

Modal logic is not the name of a single logical system; there are a number of different logical systems that make use of the signs ‘2’ and ‘3’, each with its own set of rules. Each system reflects a different understanding or conception of ‘2’ and ‘3’, or the logical properties of necessity and possibility.

## Why is it called a modal?

Modal vs Modeless

We call this type of element “modal” because it introduces a secondary “mode” — or user interface — to the web page on which it appears. A modal window disables most of the page and requires users to focus on a specific window before continuing.