“Informal Logic” I thought there was no such thing, so I did what every intelligent person does, I Googled it (grin) it turns out that there is, but it is not what either of you are saying it is…
Informal Logic is using everyday language to explain “formal Logic” informal Logic does not allow for the skipping of steps in a logical conclusion, rather it requires those steps be explained in the language a six year old could understand.
The Stanford encyclopedia of Pilosophy (http://plato.stanford.edu/entries/logic-informal/ )
Says “Though informal logic is sometimes portrayed as a theoretical alternative to formal logic, the relationship between the two is more complex than this suggests. While the attempt to teach good reasoning and critical thinking is inevitably couched in natural language, research in informal logic may employ formal methods and one could argue that the informal accounts of argument in which informal logic specializes can in principle be formalized. Recent work in computational modelling, which attempts to implement informal logic models of natural-language reasoning, suggests that defeasible (non-monotonic) logic, probability theory and other non-classical formal frameworks may be well suited to this task.”
Wikipedia has a much simpler explanation (http://en.wikipedia.org/wiki/Informal_logic )
Informal logic or non-formal logic is the study of arguments as presented in ordinary language, as contrasted with the presentations of arguments in an artificial, formal, or technical language (see formal logic). Johnson and Blair (1987) define informal logic as "a branch of logic whose task is to develop non-formal standards, criteria, procedures for the analysis, interpretation, evaluation, criticism and construction of argumentation in everyday discourse."
So, there is such a thing as informal logic, and it has to follow the same form as “Logic” just with a dumbed down vocabulary.
Everybody happy? I didn’t think so…
I appreciate the fact that you took some time to do research, but I disagree with your conclusions, it has nothing to do with the vocabulary. Let me make it even more simple than Wikipedia made it. Formal logic is deductive, and informal logic is inductive. If you can prove the premises in formal logic, then the conclusion is indisputable. On the other hand, informal logic is inherently uncertain.
Here's an example of formal logic (you know this one):
All men are mortal
Socrates is a man
Socrates is mortal
If you prove 1 and 2, 3 follows automatically.
Here's an example of informal logic:
We were told that we went to Iraq because there were weapons of mass destruction.
There were no weapons of mass destruction in Iraq.
Therefore, our government lied to us.
You can see what's going on here. Even if you do prove that points 1 and 2 are true, point 3 doesn't follow automatically, as it would if we were utilizing formal logic. Formal logic is seldom used, because it's impractical.