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Types of argument (English)

Types of arguments (English)
In general, two main types of argument are distinguished: inductive arguments and deductive arguments.

When reasoning inductive, a person starts with a specific statement in order to make a projection to a general statement / conclusion.  In other words, one or a few statements should make it likely that the conclusion is correct. Likely, so you cannot be 100% sure. Even if the statements are true, the conclusion still can be false. You should therefore always ask: "alright, but is there no exception?". Therefore, you should always pay attention when someone is arguing inductive. Especially moral debates and speeches are known for their inductive character.

Inductive arguments are evaluated as strong or weakAn inductive conclusion is strong if the reasoning seems reliable. If the conclusion improbably follows from the statements (premises) then the argument is called weak. A conclusion is sometimes called cogent when the statements in the premises are true and the reasoning is strong.

The most common form of inductive reasoning is the generalization: based on a limited number of cases a general statement is correct.

Example weak inductive reasoning (1)
Argument: I know two customers living in that neighborhood that pay badly 
Conclusion: (So) If you know someone from that neighborhood he will probably not pay.

Example strong inductive reasoning (2)
Argument: I know hundreds of poorly paying customers in that neighborhood 
Conclusion: (So) If you know someone from that neighborhood he will probably not pay

In a deductive argument the truth of the conclusion necessarily follows from the truth of what is claimed. In a deductive argument a "yes, but ..." regarding the reasoning is not possible.

If a speaker makes a deductive argument, the reasoning is by definition valid (regardless the truth of the propositions). The derivation is correct.

Standard example valid deductive reasoning (1)
If it is raining then the street is wet (general rule) 
It is raining (specific statement) 
(So) The streets are wet (conclusion)

Example not valid deductive reasoning (2)
If it is raining then the street is wet (general rule)
The street is wet (specific statement) 
(So) It is raining (conclusion)

The second argument is not valid because the streets can be wet for some other reasons. For example, children are playing with water. Now it may seem that I add new information. So you might say that the first example (the valid deductive argument) is also false? What if the streets were covered? In that case the street will not get wet!

Yet, these arguments situations differ. In the first deductive example, If you state that the conclusion is false because the streets can be covered for example, you say that the first statement is not true (if it rains the street is wet). In the second deductive argument the situation is different. The reference to the children playing with water can be made without the general norm (if it is raining, the street is wet) being false.

A deductive argument is valid if the derivation is correct. This does not mean that the statements are true. If the statements are true then the deductive argument is called sound. 

The following example will illustrate this:

Example valid, but unsound deductive argument
If you study hard, you always get a good grade (general rule) 
You study hard (concrete statement) 
(So) You get a good grade (conclusion)

This deductive argument is valid. But whether the first statement in this argument (the general rule) is true is very doubtful. Is it really true that if somebody studies hard he or she will always gets a good grade?

In short, in deductive reasoning the conclusion necessarily follows from the statements made. Of course we still can discuss about the statements that are made but the reasoning itself is correct..

Examples of inductive and deductive reasoning
Inductive: I have only seen white swans, therefore all swans are white
Deductive: My uncle has only black dogs. Hazer is also a dog of my uncle. So Hazer is black.
In the inductive argument the statement can be factually correct. Perhaps the person in question has indeed only seen white swans. We should accept this statement. Yet, the conclusion is weak (there are black swans). It is just a coincident that this person has never seen a black swan.

Inductive and deductive reasoning are sometimes summarized as:
Deductive reasoning: reasoning from the general to the particular
Inductive reasoning: reasoning from the particular to the general