Before pressing on with my posts on common sense, it is worth taking a moment to think a little about logic and argument. There are two kinds of argument forms: deduction and induction. These are easy to look up in Wikipedia but not so easy to use in practice and often students get in a mess over them, particularly in projects or dissertations.
1. A deductive argument guarantees that the conclusion is true if the premises are true. For example:
If your salary is greater that £5000 and your Tax code is CQ199 then you are entitled to a 10% rebate on your salary.
2. An inductive argument makes it probable the conclusion is true if the premises are true.
It has rained every Thursday for the last 5 weeks, therefore it will rain this Thursday.
Three crucial elements are involved:
- meaning an argument is sound if and only if the argument is valid and all of its premises are true. For instance:
All men are mortal.
Socrates is a man.
Therefore, Socrates is mortal.
The argument is valid (its form) and the premises are in fact true, therefore the argument is sound. The following argument is valid but not sound:
All organisms with wings can fly.
Penguins have wings.
Therefore, penguins can fly.
Since the first premise is actually false, the argument, though valid, is not sound.
Not Begging the Question
- that is the reason you believe the premises to be true MUST be independent
of the conclusion otherwise you can always guarantee a particular conclusion. For example, if I say "Either God exists or I'm a monkey's uncle, I am not a monkey's uncle therefore God exists. The ONLY reason this works is that the you believe the first premise '..God exists' but obviously that is ALSO the conclusion. People fall into this trap because they want to believe the conclusion more than you want the truth.
The examples I have used are simple but the arguments you may want to use or understand may be much more subtle and you may miss the fact they are badly formed and have seemingly plausible premises. The trouble I suppose is that often we either don't want to know the truth because it upsets our belief or we are so desperate to 'prove' that we are right we in essence lie to ourselves or suppress our own misgivings. In the long run these kinds of delusion can be very damaging to our thought processes.
In life we are often confronted with arguments where the premises are not necessarily 100% certain - does God exist, is the Bible the Word of God, does my wife love me... In these situations one considers whether the argument is more plausible than its denial - therefore, in general, for an argument to be a good one, we don't require 100% certainty of the truth if the premises. Of course what one person regards as plausible another may totally deny.
One can present a bad argument for a true conclusion. A person may reject your premise because of misinformation, or ignorance of the evidence, or a fallacious objection or the person does not like the conclusion.