# Do items on a list have to follow the order/logic of the previous one?

##### Asked by: Relux Lockyer

## What are the rules of first-order logic?

**An existential introduction** is also known as an existential generalization, which is a valid inference rule in first-order logic. This rule states that if there is some element c in the universe of discourse which has a property P, then we can infer that there exists something in the universe which has the property P.

## Is first-order logic consistent?

By PROPOSITION 3.5 we know that **a set of first-order formulae T is consistent if and only if it has a model**, i.e., there is a model M such that M N T. So, in order to prove for example that the axioms of Set Theory are consistent we only have to find a single model in which all these axioms hold.

## What is the difference between first-order logic and second-order logic?

Wikipedia describes the first-order vs. second-order logic as follows: First-order logic uses only variables that range over individuals (elements of the domain of discourse); second-order logic has these variables as well as additional variables that range over sets of individuals.

## Is propositional logic the same as first-order logic?

Key differences between PL and FOL

Propositional Logic converts a complete sentence into a symbol and makes it logical whereas in First-Order Logic relation of a particular sentence will be made that involves relations, constants, functions, and constants.

## What is first-order logic examples?

Definition A first-order predicate logic sentence G over S is a tautology if F |= G holds for every S-structure F. Examples of tautologies (a) ∀x.P(x) → ∃x.P(x); (b) ∀x.P(x) → P(c); (c) P(c) → ∃x.P(x); (d) ∀x(P(x) ↔ ¬¬P(x)); (e) ∀x(¬(P1(x) ∧ P2(x)) ↔ (¬P1(x) ∨ ¬P2(x))).

## Why do we need first-order logic?

To generalise, first-order logic **allows us to get at the internal structure of certain propositions in a way that is not possible with mere propositional logic**. The possession or non-possession of important logical properties turns on the precise nature of these internal structures.

## What is the difference between first order and higher-order logic?

In mathematics and logic, a higher-order logic is a form of predicate logic that is distinguished from first-order logic by **additional quantifiers and, sometimes, stronger semantics**.

## Which is more expressive between first-order logic and propositional logic?

PL is not sufficient to represent the complex sentences or natural language statements. The **propositional logic has very limited expressive power**.

Basic Elements of First-order logic:

Constant | 1, 2, A, John, Mumbai, cat,…. |
---|---|

Function | sqrt, LeftLegOf, …. |

Connectives | ∧, ∨, ¬, ⇒, ⇔ |

Equality | == |

Quantifier | ∀, ∃ |

## How do you translate a sentence into first-order logic?

*Bill takes analysis if an namely if you will not take geometry up with bill takes analysis no geometry. But not both at the same time those two vasilich. Night. So she throws in a bill Kabila crow.*

## How do I translate English to logic?

*So if you have the sentence dogs aren't people you'd symbolize this as not d because all of your propositions should be in the affirmative. And then you use the negation to represent that not.*

## How do you translate sentences into predicate logic?

*So something like jeffrey is happy again we could establish our keys. And we could say okay lowercase j is jeffrey.*

## What do you mean by propositional logic?

Propositional logic, also known as sentential logic, is that **branch of logic that studies ways of combining or altering statements or propositions to form more complicated statements or propositions**. Joining two simpler propositions with the word “and” is one common way of combining statements.

## What is the difference between proposition and propositional logic?

A quantified predicate is a proposition , that is, when you assign values to a predicate with variables it can be made a proposition.

Difference between Propositional Logic and Predicate Logic.

Propositional Logic | Predicate Logic | |
---|---|---|

3 | A proposition has a specific truth value, either true or false. | A predicate’s truth value depends on the variables’ value. |

## Which of the following is not a proposition in logic?

Solution: (3) **Mathematics is interesting**

Mathematics is interesting is not a logical sentence. It may be interesting for some people but may not be interesting for others. Therefore this is not a proposition.

## How do you identify if it is a proposition or not?

We define a proposition (sometimes called a statement, or an assertion) to be **a sentence that is either true or false, but not both**. The following sentences: Barack Obama is the president of the United States. 2+3=6.**Explain why the following sentences are not propositions:**

- x+1=2.
- x−y=y−x.
- A2=0 implies A=0.

## What is a proposition that is always false?

A compound proposition is called **a contradiction** if it is always false, no matter what the truth values of the propositions (e.g., p A ¬p =T no matter what is the value of p.

## Can an opinion be a proposition?

We call such opinions propo- sitional opinions. **A propositional opinion is an opinion that appears as a semantic proposition, generally functioning as the sentential complement of a predicate**.

## What is the difference between statement and proposition?

The difference is that **statements merely express propositions**. So a statement is “true” in virtue of the proposition it expresses being true. That is why only propositions are truth-bearers, while things like statements, thoughts, or ideas are not.

## What is the distinction between a logical statement and a logical form?

In logic, **logical form of a statement is a precisely-specified semantic version of that statement in a formal system**. Informally, the logical form attempts to formalize a possibly ambiguous statement into a statement with a precise, unambiguous logical interpretation with respect to a formal system.

## What distinguishes a sentence from a statement in logic?

Sentences and Statements

**Statements are logical entities; sentences are grammatical entities**. Not all sentences express statements and some sentences may express more than one statement. A statement is a more abstract entity than even a sentence type. It is not identical with the sentence used to express it.

## What is sentence in bearer of truth?

In classical logic a sentence in a language is **true or false under (and only under) an interpretation** and is therefore a truth-bearer. For example, a language in the first-order predicate calculus might include one or more predicate symbols and one or more individual constants and one or more variables.

## What is empirical truth?

Definition of empirical truth

: **exact conformity as learned by observation or experiment between judgments or propositions and externally existent things in their actual status and relations**. — called also actual truth, contingent truth.

## What is rational truth?

Philosophers refer to these truths as rational or a priori truths, meaning that they are **true prior to experience**. These statements can take the form of two equal sides, like an equation, or the statement “A spinster is female and unmarried”.