Southern Illinois University Edwardsville. Deductive Concepts. Deduction vs. Deductive Form: The premises are intended to provide conclusive reasons or proof of the conclusion. Inductive Form: The premises are intended to provide compelling but not conclusive reasons for the conclusion.
Definitions these definitions are just two different ways of saying the same thing. Validity in the technical sense just defined applies only to arguments, never to individual claims. If some argument is valid, then every argument with the same structure is also valid.
If an argument has one or more false premises or it is not valid, then the argument is not sound. A valid argument must have a true conclusion. So it is possible for a valid argument to have a false conclusion as long as at least one premise is false. A sound argument must have a true conclusion. TRUE : If an argument is sound, then it is valid and has all true premises. All toasters are items made of gold.
All items made of gold are time-travel devices. Therefore, all toasters are time-travel devices. Obviously, the premises in this argument are not true. It is easy to see that the previous example is not an example of a completely good argument. A valid argument may still have a false conclusion. When we construct our arguments, we must aim to construct one that is not only valid, but sound. A sound argument is one that is not only valid, but begins with premises that are actually true.
The example given about toasters is valid, but not sound. However, the following argument is both valid and sound:. In some states, no felons are eligible voters, that is, eligible to vote.
In those states, some professional athletes are felons. Therefore, in some states, some professional athletes are not eligible voters. Here, not only do the premises provide the right sort of support for the conclusion, but the premises are actually true. Therefore, so is the conclusion. Although it is not part of the definition of a sound argument, because sound arguments both start out with true premises and have a form that guarantees that the conclusion must be true if the premises are, sound arguments always end with true conclusions.
It should be noted that both invalid, as well as valid but unsound, arguments can nevertheless have true conclusions. One cannot reject the conclusion of an argument simply by discovering a given argument for that conclusion to be flawed. Whether or not the premises of an argument are true depends on their specific content. However, according to the dominant understanding among logicians, the validity or invalidity of an argument is determined entirely by its logical form.
One can represent the logical form of an argument by replacing the specific content words with letters used as place-holders or variables. All tigers are mammals. No mammals are creatures with scales. Therefore, no tigers are creatures with scales. All spider monkeys are elephants. No elephants are animals. Therefore, no spider monkeys are animals. All arguments with this form are valid.
Because they have this form, the examples above are valid. However, the first example is sound while the second is unsound, because its premises are false. Now consider:. All popes reside at the Vatican. Here is an example:. Strolling through the woods is usually fun. The sun is out, the temperature is cool, there is no rain in the forecast, the flowers are in bloom, and the birds are singing.
Therefore, it should be fun to take a walk through the woods now. Assuming you care about those premises, then the argument is strong. Assuming that the premises are all true, then this is also a cogent argument. If any of the premises turned out to be false for example, if it is actually raining , then the argument would be uncogent. If additional premises turned up, like there have been reports of a bear in the area, then that would also make the argument uncogent.
To critique an argument and show that it is invalid or possibly unsound or uncogent, it is necessary to attack either the premises or the inferences. Remember, however, that even if it can be demonstrated that both the premises and the intermediate inferences are incorrect, that does not mean that the final conclusion is also false. All you have demonstrated is that the argument itself cannot be used to establish the truth of the conclusion. In an argument, the premises offered are assumed to be true, and no effort is made to support them.
But, just because they are assumed to be true, does not mean that they are. If you think they are or may be false, you can challenge them and ask for support. The other person would need to create a new argument in which the old premises become the conclusions. If the inferences and reasoning process in an argument is false, that's usually because of some fallacy.
A fallacy is an error in the reasoning process whereby the connection between the premises and the conclusion is not what has been claimed. Actively scan device characteristics for identification.
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