# The logic of SEXI

13 Apr

The SEXI template is based on theories of informal logic and it helps to understand the model by making a small forray into the theory of logic.

Logic postulates certain certain reasoning structures, that when all supporting premises are true, the conclusion must invariably be true as well. A classic example is:

Conclusion: “Aristoteles is mortal”
Premise: “Aristotle is a man”
Premise: “All men are mortal”

As will be clear a conclusion can be translated into the S from our SEXI model, while a premise is an EX. In logical formulation, using our SEXI model it writes:

S: A = C
EX 1: A = B
EX 2: All B = C

It’s easy to see that when EX 1 and EX 2 are both true, then S must necessarily be true as well. This check on whether an argument is logical is important. For example take the following reasoning:

S: “It has rained”
EX 1: “The streets are wet”
EX 2: “When it rains the streets get wet”

Although this reasoning makes sense, it is logically invalid for the reason that other causes could have led to the streets being wet. Looking at the logical formulation shows where it goes wrong:

S: A
EX 1: B
EX 2: A => B (the arrow reads as ” then”)

As this shows you can conclude from the fact that it has rained that the streets must be wet, but not the other way round.

There are many theories and schemata’s that can tell you whether an argument is valid. It’s a bit too much to deal with in a simple blog, but it does show you the importance of EX. EX not only provides the reasoning behind your conclusion, but also provides the logical validation of your argument.

Why then do we need to have I when we already have a logically conclusive argument. The answer is that logic only determines that a conclusion must be true if the explanation is true. It doesn’t say anything about the validity of the explanation itself. In theory every EX can become its own S which then needs tovbe explained by its own EX. This can go on ad infinitum becoming ever more difficult to prove and at the same time more absurd as you go deeper. This is the stuff philosphers love to do and especially sceptics, as they will point out that at some point you cannot prove anything anymore.

However, from a practical point of view we do not need to go so deep. Assuming we all accept a general basis for accepting evidence, we can shortcut this endless string of reasoning by providing some empirical evidence. This is called inductive reasoning, compared to the deductive reasoning used above. By providing some empirical evidence on top of an explantion, be provide evidence that our explantion is not only logical, but also true. Together, as we have seen above, true and logically sound explanations must lead to a true conclusion.

That in short is some background on the logical basis of the SEXI model. Next we will look at what kinds of evidence can be used and how this logical expose can help you refute arguments of your opponent.