Logical reasoning and argument, few introductory points.


It’s always good to look back at the basics, and I know some folks need the lesson. For this post I’m going to talk about the general shape of a proper argument.

First I’ll start the basic structure of an logical argument. This is no single type of logic, but most logics anyone will be exposed to will follow the following format. I’m not getting into formal logic, but will be using some formal logic ideas to hopefully  help make some of this clearer.

Some number of premises.

A conclusion or conclusions.

Formally show in the following manner.

P1.

P2.

Pn. (where n is the total number of premises)

___________

C (often there is only a single conclusions and this is more manageable then trying to defend many conclusions)

or

C1

C2

Cm (where m is the number of conclusions)

 

Premises are the base for your conclusions and are what the conclusion stands on. They are the foundation, so if your drawing a big conclusion you best build a sturdy foundation

Premises can take a few different forms. Contextual statements, assumptions, and evidence.

Contextual statements set the scene. It’s it fair to say the certain conclusions can only be drawn under.

Generally such premises sound like. “In the case that…” Or “It is the case that when A happens and B happens” or a wide variety of If Then or other conditional statements. If you argument is in some way context depended they it’s in your best interest to point out clearly what the context is.

Assumptions are best called necessary evils. You ought avoid them where ever you can. Though it basically impossible to avoid them altogether, but I’ll get into that in my next post where I discuss inductive and deductive reasoning. Also never assume your conclusions. That is a horrible argument are will only convince the extremely gullible. Assumptions should only be used when unavoidable, and then only when you can defend those assumptions. If you can’t then you best take a step back and look into it deeper.

Evidence is somewhere in between assumption and context. Such premises are basically arguments in themselves, and each need case where evidence is brought in it is up to the arguer to make sure that it’s both relevant and reliable, and once again are able to defend both points. There is such a thing and strong and weak evidence. Where thing like anecdotal, hearsay, eye witlessness testimony are weak evidence, and thing like Peer reviewed research, expert testimony, and the personal writing of a person when arguing about what they thought on a given subject. Though Evidence deserves a whole post to itself so I’ll leave that for a more in depth discussion for later.

 

Conclusions:

Well these can be tricky, you have to make sure that you arguments are valid and sound.

An Argument is valid if the true premises always lead to a true conclusion. This is a fancy way of saying does your argument even make sense?

P1: It is the case that I have only seen purple eggplants.

C: Cats are the best animal.

I hope it’s clear to everyone here that this sort of argument makes no sense. The conclusion doesn’t follow from the premise, and they are independent from each other.

But the following example is also invalid because while the premise might well be true, not all eggplants are purple (some are white), so the conclusion is incorrect independent on the truth value of the premise.

P1: It is the case that I have only seen purple eggplants.

C: All Eggplants are purple.

An argument is sound if it is valid, and all of it’s premises are true. Now it is not always going to be clear if an argument is sound, and that’s why (hopefully) we argue. To determine the soundness of our and others arguments.

Now for example here is a valid and sound argument.

P1:Based on observations made by astrophysicists it’s is likely that some Planets are tidally locked with their suns. (evidence)

http://en.wikipedia.org/wiki/Tidal_locking#Bodies_likely_to_be_locked

P2: Such Planets have one side perpetually facing the sun and another in darkness rotating at a rate which prevents a day night cycle. (context)

P3: To experience sun rise and sun set on a planet. That planet needs a day night cycle. (context)

C: It is likely that some planets do not experience sun rises and sun sets.

That’s it for now. More later. I haven’t decided if I’ll talk about inductive and deductive reasoning, or evidence. I am taking suggestions though.

 

Withteeth

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