Kirby asked:

What is wrong with this statement:

When PII is re-defined, a major argument for its falseness is that we can conceive of there being two, therefore nonidentical, objects that are qualitatively indiscernible. So spatial and/or temporal dispersal becomes a good argument against redefined PII. But, if we stay with the original definition of PII, the spatial and/or temporal dispersal argument is a major argument in favor of PII. Under the original PII, perceiving two objects in different regions of space is prima facie evidence of nonidentity; if they are in different regions of space at a time, they are not identical.

Answer by Jürgen Lawrenz

I disagree with Geoffrey Klempner’s claim in his answer to this question that the PII of Leibniz is a purely logical principle, not to be misunderstood as pertaining to the physical universe. The very example quoted at the beginning (the leaves in the garden) disproves that supposition, by showing that Leibniz was (without room for hedging about) concerned with things that exist.

I also don’t consider the example of the pennies to be valid. It is an intuition pump deliberately engineered to produce a false conclusion. Where do these ‘logical’ pennies come from? If they’re not ‘in space’, then they don’t exist and the issue of PII never enters. In fact it would have been better to use two drops of water, which is at least an experience we are all familiar with. Then the PII has something of merit to contribute, namely confronting us with our notion of ‘1’.

The point with regard to Leibniz is precisely that the purely nominal status of space requires the concept of a volume to be replaced with the relational configuration of existents. These existents create what we call ‘space’ in their mutual relations, as something addressed to our perceptions. Accordingly the whole issue revolves around actualised monads, i.e. existents. The theoretical matrix for this is the multiple worlds in God’s mind prior to his choice of implementing ‘the best’ of these possible worlds.

It is easy to fall into the trap set for us by the likes of Everett or Wheeler that the unactualised world(s) in the collapse of a quantum wave train may be actual as simultaneous but unperceived worlds. This is another ‘logical’ game, conveniently forgetting (or disregarding) that the whole wave train is actual and terminated by the experimenter, who thus gains sight of only the instantaneous remnant of the wave, the rest being fatally disrupted and dispersed. Next time it rains, I invite you to make the analogous macroscopic experiment of inserting a piece of cardboard in the rain. Except in this case you get the whole picture, not a fragment per analogiam!

This comparison should alert us to the problem of dimensions, which as far as I can see is persistently kept out of sight. Leibniz arrived at his monads and his spatial doctrine from the recognition that all monads are a species of force (be careful not to read ‘energy’ here!): accordingly they are ‘simple, having no parts’ — in our language zero dimensional. Thus two or two trillion monads would occupy the same space, i.e. no space, to a Newtonian observer. Which brings us to the essence of the doctrine, namely the perceptions of the monads, each perceiving the others as ‘others’ and adjudging those which can only partially be perceived (because they are obscured by the nearer ones) as spatially more distant. But always ‘in its perceptions’. This is the basis for the PII thesis. As monads collectivise, each such collective comprising an existent would be influenced by its dominant monad to perceive other existents as spatially separate.

So in Leibniz’s canon, the PII is a physical, not a logical argument. It is physical not primarily because the term ‘matter’ is especially meaningful in the context, but because the species of force that binds collectives of monadic force together produce loci of force that are perceived by monads as coherent. If it is not coherent then there is no existent. Then the PII does not apply, nor does it apply to the unactualised monads that didn’t make it into God’s chosen world.

Obviously there is more to it than I’ve depicted here. Not least, perhaps, whether Leibniz’s God is dispensable to the argument or not. I believe it makes no difference if God is left out or replaced by a residual electric potential. ‘Look you, the situation is the same as in Macedonia’. Whatever exists, is subject to the Identity of Indiscernibles. And Leibniz’s monadology is about existence, about ‘why is there something rather than nothing?’ The world created by his God is such that no two identical objects can ‘occupy’ the same space because there is no space. But the moment we speak of relations, we need relata; and even in logic it is impossible to marry one relatum to itself!

Jürgen Lawrenz at PhiloSophos.com

Shane asked:

Could you go over David Hume’s Is-Ought problem and its application to morality?

Answer by Craig Skinner

Hume raises the is-ought issue in a brief passage which I quote selectively:

‘In every system of morality…I have always remark’d, that the author proceeds for some time in the ordinary way of reasoning…., or makes observations concerning human affairs; when of a sudden….instead of is and is not, I meet with no proposition that is not connected with an ought or an ought not. This change is imperceptible; but is…of the last consequence…for what seems…inconceivable, how this new relation can be a deduction from others which are entirely different…’ [A Treatise of Human Nature (Book 3,’Of Morals’), 3.1.1.27 (1740)].

In short Hume points out that facts (what is) can’t logically entail a value judgment (what ought to be). Reasoning from facts to value, a deductive argument from factual premises to judgmental conclusion, is invalid.

Of course an argument to an ought conclusion can be valid if we have an ought premise (with or without factual ones).

An example will illustrate:

P. Torturing animals for fun causes much suffering (a fact, an is statement)
C. We ought not to torture animals for fun (a moral value judgment, an ought statement)

This argument is invalid, exhibiting the is-ought fallacy.

To make it valid we need to add an ought premise (P2) as below:

P1. Torturing animals for fun causes much suffering
P2. Causing much suffering for fun is wrong
C. We ought not to torture animals for fun (it is wrong)

And herein lies the application to morality – what is the justification for the ought premise, in this case the justification for ‘causing much suffering for fun is wrong’.

Different moral theories suggest different justifications:

* feeling (Hume)
* reason (Kant)
* eudaimonia (Aristotle)
* consequences (Mill)
* common agreement (Rawls, Scanlon).
* divine command

To say a little about each:

Hume thinks reason can’t move us to action, only feeling, and that good action is driven by our innate moral intuitions or sentiments. We just feel that torturing for fun is wrong, and this is reinforced when we observe others’ horror and repulsion at the idea.

For Kant, it is wrong because we would thereby treat a fellow rational being as a mere means, not as an end; and torturing for fun is not a maxim a rational being could wish to be universal.

For Aristotle, it is wrong because it damages our soul, it prevents genuine flourishing, it goes against the proper ends or purposes of humans.

For Mill, we should do what makes for the greatest happiness of the greatest number, and this wont include torture for fun (there are subtle issues to be brought out here but now is not the time).

For Rawls and Scanlon, refraining from torture for fun is something all reasonable citizens would agree to, or no reasonable citizen would object to.

On divine command theory, God tells us torturing for fun is wrong (of course this just shows the weakness of the theory, for if we thought, instead, that God did command us to torture for fun, we wouldn’t think it right, we would think God wrong).

Finally, the Is-Ought fallacy is sometimes called Hume’s Law or Hume’s Guillotine, which is fair enough. But It is also sometimes referred to as the Naturalistic Fallacy (because it moves from nature (what is) to values), and this is confusing as that term is also used for attempts to define values in naturalistic terms, something Moore, with his ‘open question’ argument, unfairly accused Mill of doing in Mill’s account of Utilitarianism.

Craig Skinner at PhiloSophos.com

Steffaine asked:

How would you contrast the movie, The Matrix and ‘Meditation One: Of the things of which we may doubt’ by Descartes?

Answer by Geoffrey Klempner

Descartes in Meditation One works up to his case for universal doubt in several stages, but it is the last stage – the Evil Demon Hypothesis – that is the real show-stopper.

Why?

Descartes considers, and rejects, the possibility that my senses could always lead me astray. We learn about cases when we have been deceived by our senses, through the exercise of those very same senses.

But couldn’t I be dreaming now, and not realize this? This hypothesis is difficult to refute, if you allow that a ‘dream’ need not be disjointed and irrational. It is logically possible to have a coherent dream where, for example, I am in Sheffield, at my computer, writing a perfectly or at least reasonably coherent answer to Ask a Philosopher, even if such dreams occur only rarely if at all. Logical possibility is all Descartes needs.

This is the equivalent of the Matrix scenario. In reality, while I compose my answer, I am sleeping in a ‘pod’ having experiences fed directly to my brain by a super-computer.

The Matrix hypothesis is difficult to refute. But it still isn’t enough for Descartes’ purposes. Because, even on this hypothesis, certain key beliefs remain unchallenged. In particular, the belief that there exists a world of material objects in space. The existence of a physical world is one of the basic assumptions of the Matrix story.

That’s why Descartes takes the extra step of imaging a powerful, non-physical intelligence capable of producing the experience of ‘a world of material objects in space’ in me, even though in reality no such world exists. An evil demon.

But how ‘evil’ is this demon, really? Berkeley took Descartes’ argument for doubt and stood it on its head: nothing could conceivably count as proof of the existence of ‘matter’, because all we ever have is ‘experience’. All that exists, in ultimate reality, is God and ‘finite souls’ like us who have experiences that God produces in us. – When you look out at the world you are looking at the inside of God’s mind.

http://www.philosophypathways.com/vita.html

Gideon asked:

This is a puzzle. I dont know if you could describe it as philosophical.

Can this be done, without either A, B or C having possible grounds for complaint?

Answer by Craig Skinner

Yes it can.

This is an example of a Fair Division Problem. Division is fair if it is proportional (each of n sharers gets 1/nth) and envy-free (no sharer feels that another gets a bigger share than she did).

I wouldn’t describe it as a specifically philosophical problem, but fair division is crucial, for instance, to (amicable) divorce settlements or territorial divisions/treaties, and so is of interest to lawyers, politicians, and negotiators, as well as to mathematicians/logicians who think up solutions.

Sometimes we are dealing with continuous goods (divisible into arbitrarily small pieces, as with cakes); sometimes with discrete goods (indivisible, as with cats or cars) where we have to come up with a metric for comparison.

You describe a fair 2-person division for continuous goods (one divider, one chooser).

The 3-. 4-, 5,- … n-person procedure is an extension of this in which we have one divider/several choosers (Lone Divider method), or one chooser/several dividers (Lone Chooser method), as well as a more complicated Last-Diminisher method.

Here is the simplest, Lone-Divider method:

A divides cake into three pieces, X, Y and Z.

B and C each states her choice:

  Case 1. B chooses X, C chooses Y (or vice-versa).

So, B and C get their chosen slice, A gets Z

  Case 2. B and C both choose X (or Y).

So, X (or Y) is merged with say Y (or X) and B/C do a 2-person divide-and-choose on XY.

A gets Z.

Craig Skinner at PhiloSophos.com

Answer by Ira Allen

This is simple, as long as nobody minds odd-shaped slices.

A, B, and C are sharing a piece of cake. A makes the first cut, which cannot entirely bisect the cake; B then makes as many cuts as are necessary to produce three pieces. C chooses her piece first, A second, and B third. Because B will choose last, she is incentivized to take whatever opening cut A has made and turn it into the most equitable arrangement. If she privileges C at A’s expense, she can expect that A will get her back by leaving her with the worst piece. Because A can only make a partial cut, not entirely bisecting the cake, and because B can make as many incisions as necessary to produce a total of three pieces, there is no way for A to privilege C at B’s expense.

The one possibility that this leaves open is that B will want, for whatever reason, to put A at a disadvantage – and will not mind being similarly disadvantaged herself. Shortsighted viciousness is hard to account for in any model, though it’s arguably one of the defining features of the human.

Most puzzles of this sort rely on a principle of incomplete lines, i.e., on lines (cuts, here) that do not entirely cross from side to side of the figure (here, the cake) to be divided.

Ira Allen is a member of the Ask a Philosopher panel.

L asked:

I am currently writing an essay on the topic of the logicality of time travel and I have been researching various philosopher’s ideas on time travel. However, I am really confused over David Lewis’ well-respected article on the ‘Paradoxes of Time Travel.’ Lewis clearly shows he believes time travel could be possible and he goes on to say that time travellers would not be able to change the past. However, he admitted that one would alter the past just by being in the past.

Thank you!

Answer by Craig Skinner

Wouldn’t it be great to hand in an essay uncovering a logical howler by a famous philosopher!

Maybe next time.

You have misread Lewis. He doesn’t say one could ALTER or CHANGE the past, only that one could AFFECT it.

But you can be forgiven, for Lewis falls a little short, here and there, of his usual exemplary clarity. First, he doesn’t spell things out, contrasting altering/changing with affecting. Secondly, and having regard to your remark about ‘he admitted that one could alter the past just by being in the past’, his text is confusing, as follows (talking of the time traveller):

‘he changes the past from the unactualized way it would have been without him to the one and only way it actually is. To ‘change’ the past in this way,… it is enough just to be there…’

What he means here is that the TT, by being there, affects the past, has an effect on events, not that he changes it. There is no change to the past. Lewis contrasts here what ACTUALLY happens with what COULD HAVE happened had circumstances been different (eg had the TT not been there). In short he is alluding to counterfactuals and possible worlds. Of course he is a maestro in both of these fields, but I think they are a different kettle of fish from time travel.

It is a mistake to think that there could be different versions of the past, one that happened originally, and a new one when a time traveller goes back and takes a hand in events.There is only one past, it’s over, fixed, done and dusted. Any actions by time travellers have already been built in to the past. Simple example. Next month I go back to 1215 and am a signatory to the Magna Carta. This means that anybody who has studied the document in the last 800 years will have seen my signature on it. I affected the past (by being there, as a time traveller, taking part in the events, all those years ago), but I didn’t CHANGE the past.

You talk of the logicality of time travel (to the past). So here are my views on the two main alleged logical paradoxes.

The Grandfather Paradox

The fact that I am here means my grandfather wasn’t killed as a lad. But I could go back in time and shoot him, in which case I couldn’t exist. Contradiction, hence time travel impossible.

Not so. My grandfather wasn’t killed as a lad. So, if I were there as a time traveller, I didn’t succeed in killing him. Certainly, if I tried repeatedly, a series of amazing freak accidents would have occurred: the gun jams on my first try; bullets turn out to be blanks on second try; I fire at the wrong boy on my third try, etc. All very strange, but then time travel is strange so we can expect some of its implications to be strange.

The story of the history student is another amusing example. Appalled by the carnage of the First World War, learning that it was triggered by the assassination of Archduke Ferdinand, she resolves to go back and prevent it. She studies all the archives, knows exactly where the assassin will be etc, goes back, approaches him, then trips and bumps into the assassin, who was a poor shot and would have missed, nudging his arm so that the line of fire now finds its mark. Far from preventing, she has triggered the war. Horrified, she later goes back to stop her other self from tripping, but her attempt just causes the trip, and so on.

The only way in which I could go back and kill my grandfather is if time is branching or there are parallel universes. Here I go back, kill the old boy, and the universe divides into two, one where I dont exist, the other where I came from. Alternatively my travel takes me to a parallel universe just like ours up to the time of my arrival but with a different future in that I kill the old boy and never get born in that universe (but am there as a visitor to do the killing, so no paradox). However I think we can deal with the oddities of time travel without invoking branching/parallel universes.

The Free Knowledge Paradox

Rummaging in a cupboard, I find a notebook with details of how to build a time machine. After twenty years of toil I build it, then travel back twenty years to leave the instructions in the cupboard. I am a physicist tired of failed attempts to find a theory of quantum gravity. I travel two hundred years into the future, look up the accepted theory (aha!), write it all down, return and submit it to a journal whereupon it becomes the Nobel-winning accepted theory.

Where does the knowledge come from in these cases. I dont know, but knowledge is knowledge whatever its source, one could say.

For a really strange loop how about in two hundred years physics has advanced enough for time travel and for us to make universes having laws of nature of our choice, one of us travels back 13.7 billion years and sets off the Big Bang that started our universe

Incidentally, we cant change the future either, we can only affect it. Just like the past, there is only one version.

Craig Skinner at PhiloSophos.com

Answer by Shaun Williamson

I am not familiar with this article by David Lewis but I am interested in the logic of time travel. If you time travel back to the 16th century then, since you didn’t exist in the 16th century you are not really travelling back to the 16th century. You are travelling back to a possible alternative 16th century. When you return to the present you are not really returning to the present you left. You are travelling back to a possible alternative present which now contains the fact that you also existed in the 16th century. The present that you left didn’t contain this fact.

I don’t know if time travel will ever be possible but the logic of time travel is perfectly consistent as long as you accept the notion of possible alternative worlds.

Shaun Williamson developed the Ask a Philosopher cgi script question.pl. He did his postgraduate studies on the philosophy of Wittgenstein.

Answer by Geoffrey Klempner

I glanced at the article by David Lewis when I wrote my Afterword to the reprint of David Gerrold’s sci-fi time travel classic The Man Who Folded Himself but didn’t read it properly. As a result I completely missed the point that Craig has picked up on, that time travel that avoids the grandfather paradox is logically possible without positing alternative worlds.

That’s what comes from being lazy. Mea culpa. My bad.

Alternative worlds are still the only way to go if you want to have fun changing the known facts of history — such as prevending Kennedy’s assassination or the attack on the Twin Towers. But all you would be doing, as I noted in my essay, is saving Kennedy or the people in the Twin Towers in an alternative world, not the original one.

Let’s say your brand new Apple tablet which you put on the dinner table mysteriously disappears. 50 years ago a strange object (which we would today recognise as an Apple tablet) materialised in a diner in Nebraska, and was subsequently taken to Area 51 where it was studied as a possible alien artefact.

That’s how time travel works. The time traveller disappears and reappears (from their perspective) in the past. In real-time, however, the event of the time traveller materialising in the past preceded, as it must, the event of the time traveller pressing the button and disappearing.

http://www.philosophypathways.com/vita.html

Joanna asked:

Hello.

I am Joanna and I am 8. My mum found this site for me because I really want to know how I can be sure that everything is actually real and that the things I can see and hear and touch and smell and taste are not just me imagining everything? And how do I know that my mum is real (even though she helped with the typing) and that I am even real? Thank you for helping me with this question because it is making it hard for me to get to sleep at night.

Answer by Nathan Sinclair

Hello Joanna,

Like you, lots of clever people have worried about this question. In ancient Greece there was a man who thought there was no reason to believe anything he saw or touched was real, and the story goes that his friends spent a lot of time pulling him back from walking off cliffs and in front of chariots and so on.

More recently, about 350 years ago, a French philosopher called Descartes (said: DAY-CAR) tried to work out why we should believe that what we see is real, and he thought he found the most basic truth on which everything else we know depends. This basic truth is the famous saying ‘I think therefore I am’. Even if everything you see and feel isn’t real, your sights and feelings are still real themselves, and from this basic truth Descartes thought he could give reasons to believe everything else. His argument was that since I exist something better and smarter than me must have made me, and that something must be God and God wouldn’t make me see and feel things that aren’t real. If you think this argument for God isn’t very good you are not alone. Lots of Descartes’ friends thought this argument was so bad that Descartes didn’t really mean it and secretly didn’t believe in God at all. But without a good reason to believe in God Descartes doesn’t have any reason to believe what we see and feel.

Nowadays many philosophers think the reason for believing that what you see is real is that it is the best explanation of your seeings and feelings (your experiences). If your mum existed and your eyes and ears worked that would explain why you heard your mum telling you it was time to go to bed at night, and saw her looking for you if you didn’t answer. It seems really unlikely that you would have a hallucination as complicated and as organised as what you see and feel.

I don’t think the appeal to ‘best explanation’ is much good at all, I don’t know how to judge explanations and I suspect its mainly just fitting in with what you already know. Instead lets look at two suggestions I find helpful

1) Your experiences are so complicated there has to be something behind them.

Lets try a simpler question for a moment: How do you know there is more to your computer than what you see on the screen? Well, when you close a window on your computer and then open it later the same stuff appears in it. That stuff wasn’t shown anywhere but the computer had to remember it, so wherever the computer stores that information isn’t being displayed, so the computer must have some hidden parts that aren’t shown on screen. Well maybe it just stores stuff, so there is nothing more in your computer than what is on screen at some time or other. But that can’t be right because sometimes the computer does complicated calculations. Calculations so complicated that is has to store intermediate results on the way to working out the full answer. (Something like the way you might write down part of a sum on the way to working out the final answer to a maths problem, but so complicated that there is no way the final answer can be worked without storing intermediate results along the way.)

In the same way, provided you believe that there are complex patterns in your experiences, provided you believe that when you open your eyes next you will see your hands and the room around you and so on, then you must believe in the external world (the external world is where the world writes down its intermediate answers while it works out what to show you next). To say it in a negative way, if you don’t believe in the external world then you can’t believe that the world works really hard to figure out what to show you next, the world isn’t doing really hard calculations (how fast does a ball fall, just where will rainbows appear and so on) and the complex patterns you think you see in the world really aren’t there and there is no reason to think that you will go on seeing things fall down when you let go of them, the sun rise in the east tomorrow, your mum say ‘Good Morning’ to you tomorrow and so on (your experiences are like random dots that happen to make a picture but really they are just random and the picture will get wiped out by the next lot of random dots) — No real world, no complex patterns! To say it in a positive way, if the patterns in what you see and feel are real then what you are seeing/feeling is so complicated that there must be a real world behind them where those patterns are worked out.

2) You don’t start from nothing.

The way you and Descartes set up the problem, it seems like we need something fundamental that can’t be doubted to show that the world is real (or the patterns we see are genuine patterns). Maybe if we started not believing anything there is no way we could ever learn anything. (Maybe if we were stuck at the bottom of a well with no climbing equipment we could never climb out and go buy some climbing equipment.) But that doesn’t matter because we don’t start believing nothing, we start with lots of beliefs and we change them in response to what we experience. We are not like builders building a new house on a vacant lot, we are like renovators who move into an existing house and then do it up to make it nicer. Given that you already believed in the external world what new reason is there to change your mind and reject it? This is not simply a matter of which belief got in first, but of recognising that you must start from where you are now. This doesn’t really answer your question but suggests that the question didn’t accurately reflect the real problem we face which is working out what we should believe next GIVEN what we see/feel AND what we already believe in now.

These are the things that let me sleep at night and not worry if my children are real or if they are going to be there when I get up in the morning, I hope they help you too.

Nathan Sinclair recently joined the Board of the ISFP. He has a PhD in Philosophy from the University of Sydney.