A Layman's Explanation of Logic

[Eternal_Freedom]

Recently, I have been trying to explain what logic is to my younger cousin who is, to be fair to her, not the brightest cookie in the jar. Lately she has been asking me lots of questions (because surely her bigger, older, University-student cousin must know) and I have tried my best to answer in terms she woudl understand, as she has no scientific training or education beyond GCSE.

The other day, she asked me to explain to her what logic is. I found myself stumped. I am often told I am a very logical person, but I find I cannot giver her a simple definition of what logic is.

So, SD.net, what is logic? In layman's terms.

[darthdavid]

Logic is the act of taking known information and determining things that must be true or cannot be true given what you know. You should make sure to note that it's entirely possible to be completely wrong even if your reasoning is perfectly logical because logical conclusions are only as good as the known information they're based off of.

[Starglider]

Logic is the act of taking known information and determining things that must be true or cannot be true given what you know. You should make sure to note that it's entirely possible to be completely wrong even if your reasoning is perfectly logical because logical conclusions are only as good as the known information they're based off of.

Strictly that's truth-functional propositional logic. Multivalued logic can make statements about likelihood, the most general form being Bayesian probability calculus which specifies the theoretically optimal* way to do inference, even with uncertain information.

* Although computationally intractable for non-trivial cases.

[Eternal_Freedom]

Starglider, while that's fascinating it's of no help in forming a layman's explanation. Darthdavid, that's very helpful indeed, that should explain things neatly. Thank you.

[Sriad]

Generally, lay person's logic can be expressed as variations on "If [a] then " or "If [a] is [true/false] [and/or/but] is [true/false] [...], then [n] is [true/false]" using real world conditions for a, b...n. Basically, "if-then" statements are an easy way to understand logic.

The concept of a Truth Table is probably not too advanced for her with coaching, but that's probably something up to you to determine. http://www.cs.colostate.edu/~cs122/tut_2.php is a nice little tutorial on them, but it has those scary arrows and carroty logical operators. It might be good to go through something like that with your guidance though.

[mr friendly guy]

I think of logic as the method to get to a conclusion based on your premise. You can derive a correct conclusion based on incorrect logic, eg

a) a ball thrown up will come down because my dad says so, or

Incorrect conclusion even if the logic is flawless, because your premise and information is wrong eg
a. Nelly is a pink elephant
b. Therefore some elephants are pink.

Cookie for anyone who gets this sci fi reference.

[Eternal_Freedom]

Destiny of the Daleks? The Doctor and Davros...

Anyway, thank you for the comments everyone, I had a lengthy facebook discussion this evening with my cousin and I think she is getting it. Tomorrow i'll look at truth tables.

As my cousin put it "it's sorta like maths but with ideas not numbers." We're getting there.

[madd0ct0r]

that's a pretty damn good laymans defination actually.

just so long as it dosen't lead to 'maths is too hard, therefore logic is too hard'

(even if that'd be a logical conclusion, it's based off a wrong number)

[Winston Blake]

My advice: give simple examples. Throwing long, highly-accurate definitions at kids doesn't help.

E.g. find one of those logic puzzles that has a bunch of statements like 'Jim is French but wasn't in the red house on Thursday'. Let your cousin try to solve it herself for a while, then step in and show how trivial it is by using a systematic method.

Or show her how expressions in Boolean logic can be simpified by manipulating the expressions according to simple rules, such that each new line actually means something. Venn diagrams would help here. In fact, simple Venn diagrams are a good place to start in general.

[Singular Intellect]

I'd say logic in it's simpliest form would be 'consistently validated/accurate predictions'.

[madd0ct0r]

nope. that'd be experience.

I like the 'it's math with ideas' line. Doesn't quite allow for boolean stuff (at least at low level maths) but that's quite intuitive anyway.

[Darth Wong]

How much of a layperson is your cousin? Is she comfortable with computers? If she is, then you could simply say that logic is basically the same as an IF ... THEN statement in computer language. A logical proposition can be stated as an IF ... THEN statement.

[madd0ct0r]

you don't even need to know BASIC for that - it's based off English.

IF it is raining, THEN I will take an Umbrella

All dogs have 4 legs.
IF rover is a dog THEN rover has 4 legs

[Eternal_Freedom]

Well, she is a layperson in so far as she flunked most of her GCSE's (exams taken at 16) but she is quite familiar with computers, as her father builds them for a living. I think I've got her to understand logic now, which is a good start. Once she's got that down, I can start explaining heavier things a bit easier. Especially as she found the "idea maths" interesting enough to want to learn about other maths.

And yesterday she asked me a bunch of mechanics questions she had from playing call of duty. So, thank you for all your help everyone, I think I've really succeeded here.

[Darth Ruinus]

Out of curiosity, but what are the mathematics questions that came from playing Call of Duty?

[madd0ct0r]

grenade parabolas?

[Eternal_Freedom]

Grenade parabolas, bullet velocities and energies and so on. All quite fascinating, it made me get out my old A-Level Mechanics notes to explain some of the stuff.

It's things like "why do grenade launchers fire in an arc like that?"

[madd0ct0r]

and in an argument, you can whip someone with it.

[Alerik the Fortunate]

Logic is a series of steps that allows you to determine that if you know or accept some statements as true, which other statements may or must be true or may or must be false. Then give examples.

[Legault]

The "chains of reasoning" answer that Destructionator gave is about as close to perfect as has been provided in this topic. The tricky thing about responding to the question, especially in "layman's terms," is that no element of philosophy, no matter how seemingly trivial, comes without heated controversy. People will argue that logic is anything from a gateway towards eternal truth to a secondary toolset serving higher cognitive function. Boiling this mess down to a bite-sized "chains" analogy avoids all the semantic trouble. I'd personally recommend that approach.