# Can you make a valid inference invalid by adding extra premises?

If an argument is valid, then it is an instance of a valid argument formargument formA logical argument, seen as an ordered set of sentences, has a logical form that derives from the form of its constituent sentences; the logical form of an argument is sometimes called argument form.

## Can you make a valid argument invalid?

4 If the conclusion of an argument is false and all its premisses are true, then the argument cannot be deductively valid. True! —it’s the invadility principle again! 5 You can make a valid argument invalid by adding extra premisses.

## Can an inference be invalid?

An inference can be valid even if the parts are false, and can be invalid even if some parts are true. But a valid form with true premises will always have a true conclusion.

## Can you make a logically invalid argument valid by removing premises?

(a) If an argument is valid, then you might be able to make it invalid by adding further premises. (b) You can make an invalid argument valid by removing premises. (c) If a sentence doesn’t follow from another, then its denial must.

## Does a valid argument have to have two premises?

FALSE: A valid argument must have a true conclusion only if all of the premises are true. So it is possible for a valid argument to have a false conclusion as long as at least one premise is false.

## What effect might the addition of premises to a valid argument have on the validity of that argument?

Nothing. An argument based on false premises can lead both to true conclusions and to false conclusions.

## Do all invalid arguments have false premises?

If an argument is invalid, then it must have at least one false premise. If an argument has a conclusion that is certainly false, then the argument must be invalid. If the premises and conclusion are all false, the argument must be invalid. Some invalid arguments have true premises and a true conclusion.

## Can a valid argument have false premises example?

If Elizabeth Taylor is president of the United States, then Elizabeth Taylor must be 35 years of age or older. Elizabeth Taylor is president of the United States. So, Elizabeth Taylor must be 35 years of age or older. For either example, the logic is valid but the premises are false.

## Can premises be valid?

It is important to stress that the premises of an argument do not have actually to be true in order for the argument to be valid. An argument is valid if the premises and conclusion are related to each other in the right way so that if the premises were true, then the conclusion would have to be true as well.

## Can an invalid argument have false premises and a true conclusion?

Invalidity is a no guarantee of a true conclusion when the premises are false. False premises can lead to either a true or a false conclusion in an invalid argument. In these examples, luck rather than logic led to the true conclusion.

## What is an invalid argument?

Similarly, arguments may be described as valid or invalid, but statements cannot. An argument is said to be an invalid argument if its conclusion can be false when its hypothesis is true. An example of an invalid argument is the following: “If it is raining, then the streets are wet. The streets are wet.

## What makes a premise false?

Unsourced material may be challenged and removed. A false premise is an incorrect proposition that forms the basis of an argument or syllogism. Since the premise (proposition, or assumption) is not correct, the conclusion drawn may be in error.

## What is a defect in an argument other than its having false premises?

A fallacy is a defect in an argument other than its having false premises. It refers to a defect that is difficult to be detected. An informal fallacy is a defect in the content of an argument.

## When a deductive argument is invalid it is due to a formal fallacy?

Formal fallacies occur when a standard deductive argument form employs an invalid arrangement of terms or statements. Thus, formal fallacies can be detected by inspecting the form of the argument alone. By contrast, informal fallacies can only be detected by inspecting the content of the argument.

## What it is whatever has not been proved false must be true and vice versa?

Appeal to ignorance: the claim that whatever has not been proved false must be true, and vice versa. (e.g., There is no compelling evidence that UFOs are not visiting the Earth; therefore, UFOs exist, and there is intelligent life elsewhere in the Universe.