Posted by alexandra_k on May 19, 2005, at 18:46:00
In reply to Re: (((alexandra))) » All Done, posted by Larry Hoover on May 19, 2005, at 8:48:55
There are two sides to this:
Critical reasoning / thinking
Logic
They are related... But a bit different.
Critical reasoning / thinking deals with arguments in a natural language (English or whatever) and looks at evaluating whether they are good arguments or not. Part of that process of evaluation is the formal question of validity, but then there are also a lot of other things that can go wrong (lots of 'substantive fallacies' in which the premises are false) and lots of verbal tricks to make something appear valid whereas really it is not.Logic looks solely at argument structures or forms. Typically by translating English (or whatever natural language) into a logical (artificial) language such as the higher or lower predicate calculus first.
It doesn't care whether the premises are in fact true or not because it considers every possible arrangement of truth values. Any argument that has an invalid structure is an example of a formal fallacy - and there are two ones that occurr commonly enough to be given names:
The fallacy of denying the antecedent and the fallacy of affirming the consequent.From the extract:
>Many times in the past, people have concluded that because something is logically impossible (given the science of the day), it must be impossible, period.
But that doesn't follow...
Logical possibility and impossibility is an objective matter. Basically, something is logically impossible if it describes a contradictory state of affairs. e.g.
It is raining and it is not raining.
That sentance describes a logically impossible state of affairs - so long as 'raining' means the same thing both times it occurs.
Science doesn't show us anything at all about the notion of logical possibility / impossibility / necessity.If we plug the laws of nature (of the best scientific theory we have) in as premisses and assume that they are true and see what we can and cannot deduce from them then we have what is and is not physically, or metaphysically, or naturally, or nomologically necessary / possible / impossible etc.
So IF we assume the best scientific theory of the day THEN we can deduce what must be the case in the world (according to the theory).
If the conclusion turns out to be false of the actual world then it means that one of the premises (ie some of the laws of nature that appear in the scientific theory) must be false.So... Perpeptual motion machines are logically possible. This is because there is no contradiction in the idea. If the present scientific theory is correct, however, then perpeptual motion machines are naturally or metaphysically or nomologically or physically impossible. Because the existence of perpeptual motion machines would contradict the theory.
If we found a perpeptual motion machine then that wouldn't be a problem for logic. It would be a problem for the scientific theory. We would have to revise the premises (ie the scientific theory).
>It was also believed at one time that Euclidean geometry was a universal law; it is, after all, logically consistent. Again, we now know that the rules of Euclidean geometry are not universal.
There is another theory. Same scenario. Logical consistency comes too cheap. It is easy to find. Just because something is logically consistent doesn't make it a universal law...
>Secondly, logic is not a set of rules which govern human behavior. Humans may have logically conflicting goals. For example:
John wishes to speak to whoever is in charge.
The person in charge is Steve.
Therefore John wishes to speak to Steve.
Unfortunately, John may have a conflicting goal of avoiding Steve, meaning that the reasoned answer may be inapplicable to real life.Sure we have different goals. It is an axiom of 'folk psychology' that:
People will act in such a way as to satisfy their desires were their beliefs true (this is a rationality constraint).
It is acknowledged that people have different desires (goals).
The notion is that people act from the 'strongest' goal.So:
What is the rational thing for John to do???
John has two desires.
1. The desire to speak to the person in charge.
2. The desire to not speak to Steve.If John desires more to speak with the person in charge then it is rational for him to talk to Steve.
If John desires more to not speak with Steve then it is rational for him to not speak with Steve.Logic cannot tell us what he most desires (ie what IS the case).
But it can tell us what it is rational to do GIVEN different desires.That isn't a problem for logic either...
poster:alexandra_k
thread:498245
URL: http://www.dr-bob.org/babble/social/20050513/msgs/500049.html