To begin with, recall that deductive and inductive arguments support their conclusions in different ways. A successful deductive argument makes the conclusion necessarily true; this is called a valid argument. If a deductive argument fails to provide this kind of inference, which is called an invalid argument.
A successful inductive argument only makes the conclusion probably true; in this case, it is a strong argument. If an inductive argument fails to provide this kind of inference, it is a weak argument.
Whether you are dealing with a deductive or an inductive argument, it is not enough for them to be either valid or strong. For a deductive argument to guarantee a true conclusion, it needs to be both valid and have true premises. For an inductive argument to give a probable conclusion, it needs to be both strong and have true premises.
If a deductive argument is valid and has true premises, it is a sound argument. If a deductive argument doesn’t meet this standard, then it is an unsound argument.
It should be noted that an invalid deductive argument can never be sound. This is because true premises are not enough for soundness; a deductive argument needs to both have true premises and be valid in order to be sound.
|A scientist wears glasses. Hannah is a scientist. Therefore, Hannah wears glasses.||Yes||No||No|
|Wood comes from trees. My table is made of wood. Therefore, my table comes from trees.||Yes||Yes||Yes|
|Ducks are birds. Chickens are birds. Therefore, ducks are chickens.||No||Yes||No|
The first and second arguments are straightforward. The third shows that an argument with true premises can still be unsound if it is also invalid. We know that it is invalid because it is inconceivable for a valid argument to give a false conclusion with true premises.
If an inductive argument is strong and has true premises, it is a cogent argument. If an inductive argument doesn’t meet this standard, it is an uncogent argument.
Similar to what was said of deductive arguments, a weak inductive argument can never be cogent. This is because true premises are not enough for cogency; an inductive argument needs to have both true premises and be strong in order to be cogent.
|Every world leader is a female. Elections are soon. A woman will likely win.||Yes||No||No|
|Every newspaper I've read had the correct date. The next one will likely have the correct date.||Yes||Yes||Yes|
|Blogs and the Times report the news. The Times gives reliable information. Blogs likely do also.||No||Yes||No|
Whenever you want to evaluate an argument you first need to decide whether it is deductive or inductive. If its deductive, then you need to find out if it is valid or invalid and whether it is sound or unsound. If it’s inductive, you need to find out if it's strong or weak and whether it's cogent or uncogent.
Here’s how these arguments are classified:
An inductively strong argument with all true premises
A deductively valid argument with all true premises
An inductive argument that is not cogent
A deductive argument that is not sound