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## Does the law of excluded middle apply to the principle of identity and non contradiction?

In logic, the law of excluded middle (or the principle of excluded middle) states that for every proposition, either this proposition or its negation is true. **It is one of the so-called three laws of thought, along with the law of noncontradiction, and the law of identity**.

## Can a proposition be neither true or false?

A proposition is a declarative sentence that is **either true or false (but not both)**.

## Does a proposition have to be true or false?

We define a proposition (sometimes called a statement, or an assertion) to be a sentence that is **either true or false, but not both**.

## Can a proposition be either true or false?

A proposition is a declarative sentence that is **either true (denoted either T or 1) or false (denoted either F or 0)**. Notation: Variables are used to represent propositions. The most common variables used are p, q, and r.

## What is principle of non-contradiction in philosophy?

According to Aristotle, the principle of non-contradiction is **a principle of scientific inquiry, reasoning and communication that we cannot do without**. Aristotle’s main and most famous discussion of the principle of non-contradiction occurs in Metaphysics IV (Gamma) 3–6, especially 4.

## What are examples of non contradictions?

The law of non-contradiction is a rule of logic. It states that if something is true, then the opposite of it is false. For example, **if an animal is a cat, the same animal cannot be not a cat**. Or, stated in logic, if +p, then not -p, +p cannot be -p at the same time and in the same sense.

## What is proposition and not proposition?

For example, “Grass is green”, and “2 + 5 = 5” are propositions. The first proposition has the truth value of “true” and the second “false”. But **“Close the door”, and “Is it hot outside ?”are not propositions.**

## What is a logical proposition?

A logical proposition is **any proposition that can be reduced by replacement of its constituent terms to a proposition expressing a logical truth**—e.g., to a proposition such as “If p and q, then p.” The proposition “All husbands are married,” for…

## Which sentence is not a proposition?

*There are examples of declarative sentences that are not propositions. For example, ‘**This sentence is false**‘ is not a proposition, since no truth value can be assigned. For instance, if we assign it the truth value True, then we are saying that ‘This sentence is false’ is a true fact, i.e. the sentence is false.

## What is the law of the excluded middle examples?

It states that every proposition must be either true or false, that there is no middle ground. **A typical rose, for example, is either red or it is not red; it cannot be red and not red**. But some weather forecasts, it could be argued, provide another violation of the law.

## What is the law of contradiction meaning?

Definition of law of contradiction

: a principle in logic: a thing cannot at the same time both be and not be of a specified kind (as a table and not a table) or in a specified manner (as red or not red)

## What is the principle of contradiction and its importance to ethical analysis and reasoning?

The principle of contradiction **expresses the metaphysical and logical opposition between being and its negation**. It is concisely expressed by Aristotle: “A thing cannot at the same time be and not be…” (Meta.

## What does it mean to be a law or principle of thought?

Laws of thought are **rules that apply without exception to any subject matter of thought**, etc.; sometimes they are said to be the object of logic.

## What kind of principle states that nothing exists without sufficient reason for its being and existence?

**The principle of sufficient reason** tells us that nothing exists without a sufficient reason. Every being must have a sufficient reason for its being and existence. The most important and fundamental of these principles is the principle of contradiction.

## What is an example of contradictory?

contradictory Add to list Share. A contradictory statement is one that says two things that cannot both be true. An example: **My sister is jealous of me because I’m an only child**. Contradictory is related to the verb contradict, which means to say or do the opposite, and contrary, which means to take an opposite view.

## Is an argument with contradictory premises valid?

Well, if the premises are contradictory, then they cannot all be true (that’s just what contradictory means) so they can’t all be true while the conclusion is false (the necessary condition for non-validity). So the argument cannot be non-valid, it must be valid. Thus **an argument with contradictory premises is valid**.

## What is contrary proposition?

Propositions are contrary **when they cannot both be true**. An A proposition, e.g., “all giraffes have long necks” cannot be true at the same time as the corresponding E proposition: “no giraffes have long necks.” Note, however, that corresponding A and E propositions, while contrary, are not contradictory.

## How do you prove something by contradiction?

To prove something by contradiction, we **assume that what we want to prove is not true, and then show that the consequences of this are not possible**. That is, the consequences contradict either what we have just assumed, or something we already know to be true (or, indeed, both) – we call this a contradiction.

## Does proof by contradiction always work?

So, most definitely, **NO, proof by contradiction doesn’t always exist**.

## Is proof by contradiction valid?

**yes, it is a valid line of logical reasoning** and therefore applicable to all sciences. I also admit that proof by contradiction is a valid line of logical reasoning and therefore applicable to all sciences.

## Which of the following are accepted without proof?

**A postulate**, like an axiom, is a statement that is accepted without proof; however, it deals with specific subject matter (e.g., properties of geometrical figures) and thus is not so general as an axiom.

## Which term best describes a proof in which you assume the opposite of what you want to prove?

Proof by contradiction is also known as **indirect proof**, proof by assuming the opposite, and reductio ad impossibile.

## What is the first step of indirect proof?

The steps to follow when proving indirectly are: **Assume the opposite of the conclusion (second half) of the statement**. Proceed as if this assumption is true to find the contradiction. Once there is a contradiction, the original statement is true.