So I think we encounter a difficult question with question number 9.

This one is called a necessary assumption question.

The question stem reads,

Which involving is an assumption on which the argument depends?

So this would be distinguished from a sufficient assumption,

which is quite formulaic.

And you know, like, there are sufficient assumptions in this section, I believe.

Certainly in the other section of logical reasoning.

But anyway, necessary assumptions are different.

We have lessons that talk about the vast difference that exists between these two.

But I don't suppose you need to know that to get this question right.

What you do need to know is what it means for an assumption to be necessary.

It means just that, it's necessary.

Without this assumption, the argument falls apart.

Now, it might sound easy, but you have to, there's a lot packed into that statement.

What is an argument?

What does it mean for an argument to fall apart?

And let's examine this.

The recent claims that the Tasmanian tiger is not extinct are false.

That's his conclusion.

You know, why do I say with so much conviction that's his conclusion?

It just sounds like it, right?

Like, you know, if you're going to say something like that, I want proof.

I want, I'm not just going to say, okay, all right, you're right.

You know, why?

Why do you say that these recent claims that the Tasmanian tiger still exists,

that those are false claims?

Okay, let's hear your support.

Be persuasive.

As persuasive as you can be, naturalist.

So he says,

The Tasmanian tiger's natural habitat was overtaken by sheep farming decades ago,

resulting in the animal's systematic elimination from the area.

Okay, from the area.

Since then, and then afterwards,

naturalists working in the region have discovered no hard evidence of its survival,

such as carcasses or tracks.

Okay, so these are the two premises that we have.

I'll just write, I'll try to P next to it.

And in spite of the alleged sightings, they no longer exist.

But this is just sort of like reiterative of this.

So this is not really, it's just repetition, it's redundant.

That's nothing new.

So in spite of, yeah, we already knew there were alleged sightings,

and we already know that you were going to say that Tasmanian tiger no longer exists.

Right, so this is the premise, supports conclusion.

Now, so ideally what we can do is before you get into the answer choices,

identify what's wrong with this argument.

Where's the gap?

Because the reason you want to do that is because the answer choices are not your friend.

The answer choices are systematically designed to fool you, to trick you,

to bait your prejudices, to bait your biases.

So that's just flat out true for every single logical reason in question.

If you can figure out what's wrong with the argument in the stimulus,

the stimulus is your friend.

The stimulus is where all the clues are.

This is just, like, they're all just like, you know, shiny, glittery-looking things

that draw your attention to them but are, like, deadly.

So you don't want to go into this until you're ready.

So consider the premises and why it doesn't support the conclusion

as much as the naturalist might like it to.

What do we know about the Tasmanian tiger?

Well, it was driven out of this area, and then since then,

the naturalists working in this region have discovered no evidence of survival.

Okay, so what? That just means it doesn't exist in this region.

Likely it doesn't exist in this region.

But are there other regions in the world?

Maybe, right? I mean, yes, there are other regions in the world.

Perhaps the Tasmanian tiger is just, you know, the recent sighting.

And where are these recent sightings?

Are they in this region, or are they in the neighboring region?

You see, like, that's a huge, huge gaping hole in this argument.

All right, so now let's look at the answer choices.

which means whatever the answer choices are stipulating, it must be true.

It has to be true in order for this argument to work.

In other words, what we can do is we can apply a test

where we negate this answer choice, and if we negate this answer choice

and it makes our argument fall apart, then it's the right answer,

because it's necessary.

See what happens if you try to negate it? It wrecks your whole argument.

That's why it's necessary.

So A says, sheep farming drove the last Tasmanian tiger starvation

by chasing them from their natural habitat.

Way too specific.

You look at this and you say, why does this have to be true?

Why must sheep farming have driven the last Tasmanian tiger starvation

specifically by starvation and chased them from their natural habitat?

Why couldn't sheep farming have driven the last Tasmanian tigers to extinction

because the sheep herders just went out and killed all the Tasmanian tigers?

That alternate version, which is the negation, which is one possibility

when we negate this statement, doesn't wreck this argument.

If it's true that the sheep herders were the ones that killed all the Tasmanian tigers,

this argument could still be as strong as ever.

Like, yeah, it's extinct.

B says, some scavengers in Tasmania are capable of destroying tiger carcasses

without a trace.

And this one, you're thinking, well, yeah, I suppose that must be true

because they didn't find any hard evidence of survival.

But what if their carcasses just biodegrade very rapidly?

Think about it this way.

If there are no scavengers in Tasmania that are capable of destroying tiger carcasses

without a trace, every single scavenger that eats vultures, that eat carcasses,

they always leave bones.

And despite that, we still haven't found any evidence of its survival.

No carcasses.

There does not seem to be positive evidence or at least evidence that it, in fact, is extinct.

So you see, negating this doesn't wreck our argument.

If anything, it kind of helps our argument.

has looked systematically for evidence of its survival.

And again, we just don't need this.

Why do we need every naturalist?

Every naturalist but one, Steve.

Steve decides that he's going to have a sandwich instead

while all his other naturalist friends go out and systematically look for

Tasmanian tiger's evidence of their survival.

So like 99.99% of naturalists found no hard evidence.

Does really the fact that Steve decided to stay home and have a sandwich,

does that wreck this argument?

It doesn't.

in response to loss of habitat.

And that's necessary.

This had better be true.

Because the whole premise is, our premises,

the two premises we have, are focused on this area, this region.

The fact that they probably don't exist in this region

doesn't support the conclusion that they are extinct in all regions

unless we accommodate, account for,

the fact that Tasmanian tigers do not move and adapt to a different region

in response.

Because if they did, that's precisely the whole that we talked about.

Okay, fine, in this region, the Tasmanian tigers are driven out,

and we say therefore they're extinct.

But what if they just say, you know what, this neighboring region looks nice too.

In fact, it's better than this region.

We can just come here instead and have little Tasmanian tiger babies.

You have to account for this.

Otherwise, this premise just loses all support for,

I shouldn't cross this out, I should cross out over here the support,

loses all support for the conclusion.

And this one, a lot of these answer choices are just there for you to,

I'm thinking, well, I would like for them to be experienced naturalists.

Or if they're not, I suppose that's relevant somehow.

Because what if they're not, I'm guessing they maybe can't recognize

Tasmanian tigers as well.

But the point is, none of those things matter.

They're things that we think about when we think about sightings of Tasmanian tigers.

But not whether this premise, not why this premise,

or rather I should say where this premise leaves a hole in its support for the conclusion.

We don't need this to be true.

What if they were experienced naturalists?

So, they could still be wrong.

So those who reported the sighting of Tasmanian tigers,

even if they were experienced naturalists, they could still be wrong.

This argument could still stand.

The point is we don't need this to be true.