英语论文网

One of the most common valid argument patterns is modus (ponendo) ponens. This is the pattern:

(Premise 1) If P then Q.
(Premise 2) P.
So:
(Conclusion) Q.

Example: let ‘P’ be ‘It is raining heavily’ and ‘Q’ be ‘The grass is wet.’
(Test the pattern – remember in regard to the propositional variables ‘P’ and ‘Q’, that you must use the same value for P, and the same value for Q, throughout the example.)

Now consider the following actual argument.

If global warming is a reality, Australia can expect prolonged droughts.
Australia is experiencing a prolonged drought.
Therefore: Global warming is occurring.

This is in fact fallacious; the fallacy is called affirming the consequent and it is one of two counterfeits of modus ponens. Notice that the modus ponens pattern has a premise which is conditional (also called a hypothetical), and a conditional proposition has an antecedent (the ‘if’ clause) and a consequent  (the ‘then’ clause).
In other words the pattern embodied in the above argument is:
If P then Q.
Q.
So:
P.
The above represents the pattern of an argument that embodies the fallacy of affirming the consequent. Note that just because such an argument is fallacious, it does not follow that the conclusion is false.

Here is the second counterfeit to modus ponens. Consider:

If it is raining, then the grass is wet.
It is not raining.
So:
The grass is not wet.

(But what if somebody had been hosing the lawn? (Remember hoses?))

This embodies the fallacy of denying the antecedent. Can you see why?

On the other hand, denying the consequent is not a fallacy.
Consider the pattern:

(Premise 1): If P then Q.
(Premise 2): Not Q.
So:
(Conclusion): Not P.

In fact this is a sufficiently common valid argument pattern that it has a name: modus tollendo tollens.

The final formal fallacy we will consider is known as the modal fallacy.  Any proposition must have one of three modalities. They are apodeictic, assertoric, and problematic.

Apodeictic mode: It is necessarily the case the P.
Assertoric mode:  (It is actually the case that) P.
Problematic mode: It is possibly the case that P.

I have enclosed the assertoric modal qualifier in parentheses as we normally do not use it, except to avoid ambiguity or misunderstanding. That is because we normally speak and write in the assertoric mode, making it necessary to incorporate a modal qualifier only when we depart from that mode.

Notice that there is a one-way entailment relationship among the modes. Each of the above three forms entails the one below it. But there is no valid inference pattern up the list.

The modal fallacy occurs when we wrongly incorporate the necessity with which a conclusion follows from the premise set into the conclusion itself. Compare the following side by side examples:

                (I)                                                     &nb本论文由英语论文网提供整理，提供论文代写，英语论文代写，代写论文，代写英语论文，代写留学生论文，代写英文论文，留学生论文代写相关核心关键词搜索。