Two Senses of Change

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From the course by The University of Edinburgh

Introduction to Philosophy

2936 ratings

The University of Edinburgh

Introduction to Philosophy

2936 ratings

This course will introduce you to some of the main areas of research in contemporary philosophy. Each module a different philosopher will talk you through some of the most important questions and issues in their area of expertise. We’ll begin by trying to understand what philosophy is – what are its characteristic aims and methods, and how does it differ from other subjects? Then we’ll spend the rest of the course gaining an introductory overview of several different areas of philosophy. Topics you’ll learn about will include: Epistemology, where we’ll consider what our knowledge of the world and ourselves consists in, and how we come to have it; Philosophy of science, where we’ll investigate foundational conceptual issues in scientific research and practice; Philosophy of Mind, where we’ll ask questions about what it means for something to have a mind, and how minds should be understood and explained; Political Philosophy, where we'll investigate whether we have an obligation to obey the law; Moral Philosophy, where we’ll attempt to understand the nature of our moral judgements and reactions – whether they aim at some objective moral truth, or are mere personal or cultural preferences, and; Metaphysics, where we’ll think through some fundamental conceptual questions about free will and the nature of reality. The development of this MOOC has been led by the University of Edinburgh's Eidyn research centre. To accompany 'Introduction to Philosophy', we are pleased to announce a tie-in book from Routledge entitled 'Philosophy for Everyone'. This course companion to the 'Introduction to Philosophy' course was written by the Edinburgh Philosophy team expressly with the needs of MOOC students in mind. 'Philosophy for Everyone' contains clear and user-friendly chapters, chapter summaries, glossary, study questions, suggestions for further reading and guides to online resources. Please click "Start Here" and navigate to the "Optional Reading" page for more information.

From the lesson

Time Travel and Philosophy

(Dr. Alasdair Richmond) In this module we'll think about some issues in metaphysics, a branch of philosophy that investigates the ways that reality could intelligibly be. Our case study will be the possibility, or otherwise, of time-travel. Some have thought that the apparent possibility of creating a machine that we could use to transport a person backwards in time can be ruled out just by thinking about it. But is time-travel really logically impossible? What would the universe have to be like for it to be possible? And can we know whether our universe fits the bill?

What Might Time Travel Be Anyway?7:18

Grandfather Paradoxes9:14

Two Senses of Change7:23

Meet the Instructors

Dr. Dave Ward
Lecturer in Philosophy
University of Edinburgh
Professor Duncan Pritchard
Professor of Philosophy
University of Edinburgh
Professor Michela Massimi
Full Professor
Philosophy
Dr. Suilin Lavelle
Lecturer in Philosophy
University of Edinburgh
Dr. Matthew Chrisman
Reader in Philosophy
Philosophy
Dr. Allan Hazlett
Dr. Alasdair Richmond
Dr.
Philosophy
Guy Fletcher
Lecturer
Philosophy
Elinor Mason
Senior Lecturer
Philosophy

Okay, so, so far we've covered Lewis' account of what time travel actually

involves, and we've covered Lewis' attempt at trying to diffuse the appeared

grandfather paradoxes. So, so far, the account is this: travel

into the past is logically possible provided that what the traveler does in

the past is consistent with the history whence the traveler comes.

Now at this point, you might be thinking well hang on, if the traveler's actions

already exist in the past, and some say it's before the travelers set sight, or at

least if the traveler's actions exist at external times earlier in the traveler's

departure, how could the traveler have any impact on the past.

People sometimes hear Lewis' analysis and think, well surely the traveler is just a

sort of pre-programmed robot, completely pre-determined to go through a completely

rigid set of actions. Or what still, people might think that a

traveler in the past, is doomed to be some sort of ghost, forced to witness events,

but be powerless to intervene. Well Lewis thinks that it's possible for a

traveler be really concretely present in the past, a proper functioning human agent

with intentions, and wishes, and choices, and to make a difference to the past.

We have to be careful how we imagine the impact of a traveler in the past.

Lewis distinguishes between two senses in which it could be said that a traveler

could change the past, what I'm going to call replacement change and counterfactual

change. In a nut shell, Lewis says that a traveler

in the past cannot effect replacement changes, but can effect counterfactual

changes. Well what's a replacement change?

Consider a perfectly ordinary object, like a glass.

If I were to drop a glass, from waist height, onto a concrete floor, and the

glass shatters, I would have replaced an intact glass with a set of glass

fragments. I would have affected a replacement change

in events, there was an intact glass, the intact glass is shattered, the intact

glass has gone away. And in its stead, it's been replaced by, a

set of glass fragments. Now Lewis thinks, that replacement

changes, can happen to concrete objects, but not to times.

You can't replacement change, any time, past, present, or future.

Suppose you make a plan to meet a friend for lunch at 12 o' clock at a certain

restaurant. And then, you get a text from your friend

saying, I'm sorry I can't make lunch today, can we meet tomorrow?

Well that hasn't replacement changed the future.

It's not that you did in the future meet at a certain restaurant and then that

future somehow went away. So Lewis says, yes, you can't affect the

replacement changes in the past, but you can't affect the replacement changes in

the future either. Replacement changes can only happen to

concrete objects. You can replace a concrete object, like an

intact glass, with a set of glass fragments, but concrete objects are not

the same as times. So that's replacement change.

Counterfactual change, maybe a little bit harder to get a handle on, but

counterfactual change is the impact that you have, assessed in terms of what would

have happened, counterfactually, if you hadn't been present.

One of the things that enabled me to be on time for this session this morning, was

that my alarm clock went off on time. But if the alarm clock hadn't gone off, I

would have been late, so I can assert the counterfactual, if my alarm clock had

broken I wouldn't have been on time. So when my alarm went off, clearly had an

impact on my ability to attend this session on time.

If my alarm clock had broken, I would have been late.

So, in a sense, the alarm has changed the course of my day.

But that change is not to be assessed in replacement terms.

It's not that there was an original version of events, or my alarm clock

didn't go off and I was late, and then somehow my alarm clock did go off and

history was replacement changed and I was on time.

Rather, the impact the alarm clock had can be assessed counterfactually.

This morning only happened once, and it happened with my alarm clock going off on

time. But if it had happened differently,

history would have unfolded differently. Another example.

Historians who treated the period, not least Arthur Wellesley, the Duke of

Wellington, maintained there's a crucial factor in determining the outcome of the

battle of Waterloo, was the arrival in the late afternoon at the battle Of Prussian

forces under the command of Field Marshall Blucher.

Wellington, himself, frequently said that if Blucher had been late, Napoleon would

have won. So that's clearly a counterfactual

conditional: If Blucher had been late, Napoleon would have won.

Again, it's not that Blucher made a replacement change to the battle of

Waterloo. It's not that Waterloo originally issued

in a French victory and then Blucher's forces arrived and the French victory

somehow was made such that it never was and an Allied victory took its place.

Waterloo happened only once, with a victory for the Allies.

But an important factor in that victory, was the arrival of Marshall Blucher.

So we can see that Blucher's arrival changed the course of history, but it

changed it in the counterfactual sense, not in the replacement sense.

Okay, we've got two senses of change, placement change, counterfactual change.

Lewis maintains that time travelers can have an impact on the past, in the

counterfactual sense. The presence of a traveler might make

history different from what it would have been if the traveler hadn't been there.

Going back to my attempt at assassinating Hitler.

Suppose my time machine deposits me in Vienna in 1908 with a great flash of

light. And I've arrived so close to Hitler that

Hist-, that Hitler sees a flash of light, and recoils.

He steps back in shock, out of the path of a tram that would otherwise have cut him

down. In this case, I could assert the

counterfactual, if I hadn't traveled back in time, Hitler would have died.

So in this case, I clearly had a counterfactual impact on history.

I have, albeit unwittingly, been partly responsible for Hitler's survival.

So it could well be, that the course of history could consistently contain the

kinds of factual impact of the presence of time travelers.

Another example, suppose that I travel back to 1864, and I bump into Lincoln?

Lincoln's about to give the world famous words, that of the Gettysburg Address, but

he's unsure of which version to give. He has a choice between the famous version

history recalls and another version. And I say to him, Abe, go with the version

that starts, these great resonant sentences, about how this nation was

conceived in liberty. That will go down very well.

And Lincoln takes my advice. And the other version, of the speech is

binned. But suppose if I hadn't intervened,

Lincoln would have recited a different version of the Gettysburg Address.

Well, I could have had an impact on history, history is different as a result

of my efforts. But I've not replaced anything.

I've not made one version of the Gettysburg Address disappear, and another

version take its place. The Gettysburg Address happens once and

once only. But I've still changed the course of

history.

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