# How to define ‘impossible’ using propositional modal logic?

## What is modal proposition in 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?

For example, when A is ‘Dogs are dogs’, ◻A is true, but when A is ‘Dogs are pets’, ◻A is false.) Nevertheless, semantics for modal logics can be defined by introducing possible worlds. We will illustrate possible worlds semantics for a logic of necessity containing the symbols ∼,→, and ◻.

## Is modal logic true?

In the most common interpretation of modal logic, one considers “logically possible worlds”. If a statement is true in all possible worlds, then it is a necessary truth. If a statement happens to be true in our world, but is not true in all possible worlds, then it is a contingent truth.

## What are the types of modal logic?

modal logic, formal systems incorporating modalities such as necessity, possibility, impossibility, contingency, strict implication, and certain other closely related concepts.

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## Where is propositional logic used?

It has many practical applications in computer science like design of computing machines, artificial intelligence, definition of data structures for programming languages etc. Propositional Logic is concerned with statements to which the truth values, “true” and “false”, can be assigned.

## What is modal logic in computer science?

Modal logic is a widely applicable method of reasoning for many areas of computer science. These areas include artificial intelligence, database theory, distributed systems, program verification, and cryptography theory.

## Who invented propositional logic?

Although propositional logic (which is interchangeable with propositional calculus) had been hinted by earlier philosophers, it was developed into a formal logic (Stoic logic) by Chrysippus in the 3rd century BC and expanded by his successor Stoics. The logic was focused on propositions.

## Is modal logic difficult?

The reason we want to utilize modal logic is to precisify ordinary language. Ordinary language is notoriously ambiguous and the analysis of ordinary language modal operators is fraught with difficulty. By regimenting our discourse into formal (quantified) modal logic we can eliminate some of these ambiguities.

## Which of the following is the correct sequence of logical connectives in propositional logic?

Of its five connectives, {∧, ∨, →, ¬, ⊥}, only negation “¬” can be reduced to other connectives (see False (logic) § False, negation and contradiction for more). Neither conjunction, disjunction, nor material conditional has an equivalent form constructed from the other four logical connectives.

## How do you solve propositional logic?

Quote from video on Youtube:The first one which we call a says we are both telling the truth and B says a is lying and so we want to do is try to analyze this and figure out who's telling the truth and who's lying.

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## How do you know if your proposition or not?

Sentences considered in propositional logic are not arbitrary sentences but are the ones that are either true or false, but not both. This kind of sentences are called propositions. If a proposition is true, then we say it has a truth value of “true”; if a proposition is false, its truth value is “false”.