Sound
Having good structure is only part of what makes an argument reliable. The most reliable arguments are those that we can describe as sound. A sound argument is one which has a valid structure and has true premises. A sound argument is therefore the best sort of argument to have. Since sound arguments have both a valid structure and true premises we are also guaranteed that they will have true conclusions too.
​
The difference between an argument being sound and being valid is that valid arguments are not required to have true premises but sound arguments are.
​
If an argument is not sound we can call it unsound.
Unsound
P1 - All hats are gloves.
​
P2 - All gloves are trousers.
​
C - Therefore, all hats are trousers.
Sound
P1 - All hats are headwear.
​
P2 - All headwear are clothing.
​
C - Therefore, all hats are clothing.
The second argument is valid because the conclusion logically follows from the premises. It has good structure but isn't true which is why it is unsound. Only arguments which are valid and true can be sound. The first argument has both good structure and is true and so is sound.
​
When using arguments in philosophy you should always strive to use sound arguments as they are very reliable.
Key
Words
Sound
Unsound
Valid
Invalid
Consider the following arguments:
First
All cats are lizards.
​
All lizards are birds.
​
Therefore, all cats are birds
The first argument, while valid, is not sound. It is not sound because both the premises are false (cats are not lizards and lizards are not birds).
​
The conclusion has been correctly inferred from the premises, but we cannot depend on it because it is based on false claims.
​
The second argument has both valid structure and true premises. WE can therefore place more faith in the second argument as it is sound.
Second
All cats are mammals.
​
All mammals are vertebrates.
​
Therefore, all cats are vertebrates.
Unsound Arguments
​
Because sound arguments require two ingredients to be sound, there is therefore more than one way for an argument to be unsound.
​
An argument is unsound if it either has false premises or an invalid structure, or both.
​
Consider the following examples:
First
All parrots are cats.
​
All cats have feathers.
​
Therefore, all parrots have feathers.
Second
All parrots are birds.
​
All parrots have feathers.
​
Therefore, al birds have feathers.
Third
All parrots are cats.
​
All parrots have feathers.
​
Therefore, all cats have feathers.
All of these arguments are unsound, but each for a different reason.
​
The first is valid but its premises are false.
The second has true premises and a true conclusion but has an invalid structure.
The third has both false premises and an invalid structure.
​
Deciding whether an argument is sound or unsound isn't always easy. If you are good at critical thinking you might be able to determine if an argument is valid but you might need some factual knowledge to say whether or nor it is sound.
​
Notice , however that once you determine that an argument is invalid, the issue of assessing the truth of the premises doesn't arise.
​
All invalid arguments are unsound while only some valid arguments are unsound.
Tasks
Have a read over and complete the following tasks.
​
Copies are also on you GoogleClassroom.