# Humans and logic

Discussion in 'Human Science' started by arfa brane, Aug 17, 2015.

1. ### YazataValued Senior Member

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It's important to recognize that the phrase 'logical truth' has several technical meanings in logic.

The most common one refers to symbolic expressions and is roughly synonymous with 'tautology'.

Example: If some A's are B's, then some B's are A's

What makes this a 'logical truth' is the fact that it is true simply because of its logical form, no matter how the the variables 'A' and 'B' are interpreted.

That isn't a logical truth. If we replace 'human' and 'logical' with variables, the expression won't always remain true, regardless of the meanings that we give the variables. In this case we are ascribing a property (being logical) to individual members of a class of objects (humans). Obviously the ascription of properties to objects doesn't always result in truths.

Assuming that humans are logical now (highly debatable), I suppose we can say that it was always true in the past that humans would be logical now, and it will always be true in the future that humans were logical now.

But that's stretching logic. Conventional propositional and predicate logics are timeless and pay no attention to grammatical (past and future) tense. To rectify that, logicians have proposed tense-logics and temporal logics more generally. (There are many different alternative logics floating around out there.)

http://plato.stanford.edu/entries/logic-temporal/

Interestingly, Aristotle noted some of the difficulties that arise way back in the fourth century BCE. His classic example was 'The Sea-fight Tomorrow'. Suppose a naval battle takes place between the Greeks and the Persians. Suppose that we know after the fact that the Greeks win. Was it already true the day before the battle that the Greeks would win the next day? If we say 'yes', does that commit us to fatalism, to the view that it was always logically predetermined that the Greeks win and that the battle could have come out no other way?

http://plato.stanford.edu/entries/future-contingents/

Last edited: Aug 18, 2015

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3. ### originHeading towards oblivionValued Senior Member

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Which side of the brain do liberals use? You said before and I have forgotten.

You do know that this whole left brain right brain stuff is just pop science and has little real relevance?

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5. ### arfa branecall me arfValued Senior Member

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What if, I know this is difficult. you don't replace them with variables?

Except that humans have been doing logical things since humans appeared. That statement does not say humans are not illogical.

Why did you add the word "now", what was it that compelled you to put it in a temporal context?

Is the statement "Humans are logical" true, or false?

Last edited: Aug 18, 2015

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7. ### TrippyALEA IACTA ESTStaff Member

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Because in humans, decisions are a higher function.

My, albeit limited, understanding is that at a basic level neurons behave like AND, OR, and NOT gates. Some neurons only one input to trigger a response, some require more than one input, and others require an input to suppress activity.

If you look at the basest animal levels, and at population rather than individuals - for example, how the brain senses edges or the presence of light or sound, the responses are the same in every one and follow fairly straight forward decision trees. My recollection is that, for example, the brain has different areas for sensing edges in different directions.

Unfortunately (or perhaps fortunately) for humans decision making is a higher function, which is subject to more complex inputs. And thi isn't just true for humans either, the same complex decision making can be observed, at least to some extent in animals, for example, consider the differences in behaviour between domesticated animals and their wild counterparts. When it comes to learned behaviours and human decision making there's all sorts of other variables coming into play, But in the end these are all the result of the same logical proccesses, those same AND, OR and NOT gates. The difference is that some of them may now have multiple output states, some of them have different input thresholds, and yet others of them aren't governed by the ouputs of other neurons, but rather, their state is controlled or their behaviour is modified by the presence or absence of certain chemicals in the environment.

Imagine, for example, if we took a pair of iphone/ipod compatible ear-buds, and modified them so that the output voltage of the inline remote was dependent on the instaneous voltage in the earbuds, the ambient noise levels picked up by the microphone, and the ambient levels of carbon dioxide and ethanol in the atmosphere.

Emergent complexity from simple systems. Finally, consider the bifurcation diagram for

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A straight forward enough system that can be driven to some very complex pseudo-random behaviour. And after all, maybe that's all there is to us - maybe a different person under exactly identical starting conditions will respond the same way, but no two people respond the same way because of the sensitivity of our behaviour to its (IE Our) initial starting conditions. who knows how differently I would have turned out if I hadn't seen a kid drown and then be recussitated when I was 11 or 12.

8. ### arfa branecall me arfValued Senior Member

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Let's try something really, really easy.

The statement: "Humans are mammals", is either true or false, which means the question: "Are humans mammals?", has a yes/no answer.

Let's note carefully that the statement isn't in a temporal context. It does not say: "Today, humans are mammals", or: "1 million years ago, humans were mammals".

Ok? Or should I go a bit slower?

So if (it's true that) humans are indeed mammals, when you meet a human you're meeting a mammal. This is also true because humans have always been mammals.

Mammals have brains, therefore humans have brains. What humans know about brains is that they are specialised organs, they are the reason humans are conscious of not just the world around them, but of themselves--humans have a "theory of mind".

Are brains logical? It seems they are; the "operating system" depends on inter-neural communication and neurons communicate in some kind of code that we don't know a whole lot about. What we do know is that groups of neurons cooperate, something like a temporary "circuit" appears, or a switching network. Also, general brain activity varies between random "noise" and structured "waves"--the brain seems to be a stochastic system in which structure emerges from chaotic activity. Then there is memory, which appears to be based on a "strengthening" of connections between neurons.

Stop me if you've heard this one.

Last edited: Aug 18, 2015
9. ### iceauraValued Senior Member

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30,994
Much of that processing is done in the retina of the eye - which has claims to being part of the brain, but is usually not included.

They can be modeled, very awkwardly, by arrangements of such transistors. But so can almost everything else in the world.

Their actual behavior includes some "analog" processing and signaling (the relative and absolute levels of at least four ions are involved: calcium, chloride, potassium, and sodium), and it's worth noting that they can each possess thousands of connections to other neurons all of which operate as both input and output feeds - which is closer to "analog" structure than a standard "analog" windup clock with hands.

One must exert effort to avoid underestimating that situation - the starting conditions referred to are generated patterns of patterns of neural firing involving several hundred thousand neurons minimum: not the neurons themselves, or any state of the neurons themselves, or any combination of such static conditions, but the time-extensive patterns of the patterns of the behaviors of these neurons. The neurons are substrate, not constituent.

A thought, image, memory, etc, is an activity, a pattern of behavior in time. A whirlpool, not a pool. So the poet's comment that "in dreams begin responsibilities" is quite possibly physically, scientifically, reductionistically, technically, accurate - not poetic license, but exact description. It awaits appropriate replicable research, currently beyond our capabilities.

10. ### arfa branecall me arfValued Senior Member

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Because I can't help myself, I'm going to explore the possibility of the brain being in an illogical state.

How, first of all, does a logical system get to this state, and what is an illogical state? How does this state affect the rest of the system--the body which the brain controls?
No, hang on, I can't be bothered trying to answer those questions, so I'll just hang my hat on the opening sentence being bollocks, something somebody made up that I just can't make sense of.

But, of course, one might confuse the output of a logical system such as a brain or a computer with what's going on inside the "black box". Well, I can write programs that output "wrong answers", but I have to write them in a logical language. Ergo, um . . .

11. ### arfa branecall me arfValued Senior Member

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By golly, I really didn't expect the doubt I got in this thread.

See, the logic in the OP is propositional, there are no quantifiers; statement 2 does not say: "All humans are logical", or: "Some humans are logical". It's a bare statement about humans that says nothing about how logical, or when we first used logic. It can only be true or false. Being logic, it does not have some requirement that events or actions be included, or time.

If it is true (and I can't see that it can be false, because it also says nothing about logical acts, or "being illogical" either), then it can only be logically true, hence "always" true. In terms of a history, ours was and is always this one, in which we have logic because it's a positive adaptation, in evolutionary terms.

p.s. Note how introducing temporality with words like "sometimes", "always" etc can change the truth-value if you add some human activity (I don't know why that sounds like a summary of this thread):

"Humans are logical", is true because humans do logical things because they have logical brains.
"Humans are always logical", is also true, but:
"Humans always behave logically" is not true.

Last edited: Aug 19, 2015
12. ### DaeconKiwi fruitValued Senior Member

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"Humans are always logical" is not true because sometimes they aren't.

13. ### arfa branecall me arfValued Senior Member

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And I think it is true because those without it would most likely not survive long. Where are all the humans with brains that aren't logical? I'd say they didn't make it. I'd say they probably didn't get conceived or reach infancy either.

And I think you mean human behaviour, not whether humans are logical animals.

14. ### DaeconKiwi fruitValued Senior Member

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How would such a difference be manifested?

15. ### arfa branecall me arfValued Senior Member

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What difference?

Look a bit closer at your statement:
; "because sometimes they aren't" is your temporal correction.
The words "are always" implies activity, but it isn't there. Think about my original proposition historically: "Humans are [historically] logical", because they have survived to today, and not by f-ing around.

16. ### arfa branecall me arfValued Senior Member

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Ok, maybe it's time to try expanding on my initial proposition.

Let's consider the possibility that the logicality of humans, being evolutionary, is something that humans apply in a parsimonious manner (it's hard to think abstractly for long periods like in a physics or maths lecture). Let's assume that human history has sufficient logical behaviour in it that we've survived this far.

So there's plenty of room for logical brains to allow for a lot of illogical thinking, as long as sufficient humans have maintained the otherwise logical part of our history, since here we are.

So we now have: "Humans are logical" being "The history of humans is sufficiently logical that they are an extant species".

17. ### DaeconKiwi fruitValued Senior Member

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I'm still not sure where you're going with this.

I'm also not sure that you're using the word "logical" in the same sense as the rest of us, which is just causing most of the confusion that's apparent in this thread.

18. ### arfa branecall me arfValued Senior Member

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Well, why don't you find out? Then at least you won't be confused, and seriously who cares about the rest?

19. ### wellwisherBannedBanned

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Logic is fairly new in terms of human evolution, with logic processed in the left side of the brain. Natural instinct is more connected to the right side of the brain. The right brain is spatial and integral, with natural instinct integrating animals with nature.

Natural instinctive humans would be right brained. For logic to appear, this means consciousness had to first migrate from right to left brain before logic became something done by the will. This would make natural instinct become less conscious, until it was no longer clear what natural was. This would be reasoned instead.

We use both sides of the brain, but only one side of the brain, consciously. If humans were originally instinctive and right brained, their left brain would be unconscious and spontaneous; selective spontaneous logic. This would not be under the control of the will. They would say the gods (unconscious) were doing this for them.

If the instinctive right brained human saw a food animal, he would instinctively know how to cut off the angle using unconscious cause and effect and action and reaction. The left brained huan will plan this out in the mind instead of just act on impulse. This is newer.

20. ### arfa branecall me arfValued Senior Member

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What did our brains do before this happened?

I think there's a big problem with your statement, apart from it being a load of bollocks that you made up, brains are logical, brains have always been logical, brains are evolved organs and evolution is a logical process.
If all brains are logical, then all animals with brains are logical and behave logically (unless I see a convincing argument that brains and animal behaviours are somehow disjoint). Or animals are sufficiently logical (in their behaviour) that they survive.

Therefore I refute your statement and what follows it, since it's highly improbable that humans would exist today if they only became logical in their recent history. Instead, humans have always been logical animals.

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21. ### SarkusHippomonstrosesquippedalo phobeValued Senior Member

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There are two things being discussed here, it seems.
First, the human brain is a processing unit. It must follow rules or else it would be random, and no patterns would emerge. These rules form the basis of its "logic", and thus it could not only be said to act logically but, in a healthy human, it MUST act logically - i.e. according to those rules.
When the brain is damaged those rules might change somehow - and while it could then be said to be acting illogically, this is only in comparison to the previous (undamaged) state that we referred to as "logically".

The second thing being mentioned is the notion of logic as a philosophical field, the adherence to strict rules in rather clinical, simple (relatively speaking) situations, from which we get deductive reasoning etc.

The first refers to the operation of our brain at the minutest level of reality, including whatever quantum mechanics might throw at it.
The second refers, I think, more to what we perceive in rather macroscopic situations.

Humans are / must be logical according to the first: anything that operates in a non-random way must follow rules, rules that dictate the logic of that system.
Humans may not always be perceived to be logical according to the second, depending upon the level at which we perceive the premises, are aware of the weights and measures by which we judge the situation. We may do something that appears to others to be entirely illogical - e.g. we keep our hand over a flame until it burns our flesh, fighting instinct to do it. Sounds illogical? But if there is compulsion (e.g. a bet for £1 million) to do so then the logic might become apparent.

I have undoubtedly muddied the water - but 'twas only logical to do so!

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22. ### arfa branecall me arfValued Senior Member

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First order logic includes propositions such as "All A are B", or just "A's are B's", where the latter has an implicit universal quantifier (and please excuse the apostrophe, since logically plurals don't have one).

If either statement is true, then it is never false (there is no case of any A not being a B). There is nothing about time here, it's "just logic".

For some, possibly anthropic reason, when A = humans, and B=logical, some kind of problem appears in the logic. We think. Or maybe, some of us do.

For instance, if it is true that brains are logical and the temporal product of a logical (evolutionary) process, then "illogical thinking" is a temporal product of a logical brain. Therefore, irrational or illogical ideas are also logical in general.

So how do we tell? What informs us that some individuals ideas don't follow "normal" logic? Instinct? Our own normal, rational thinking? Emotion perhaps? That's an element that hasn't been mentioned, brains are also emotional or are the seat of emotion, as well as logic.

Last edited: Aug 20, 2015
23. ### DaeconKiwi fruitValued Senior Member

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"All swans are white", or just "swans are white" - Until you find one that is black.