## anyone with BP LG book help me out pls?

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flash21

Posts: 1536
Joined: Fri Apr 19, 2013 8:56 pm

### anyone with BP LG book help me out pls?

Pg 289, I'm just wondering why Felicia doesn't have to be included in that chain (in the contra positive) . I still don't understand from the explanation in the book, I've read it over a few times to no avail.

Thank you.

062914123

Posts: 1846
Joined: Sun Apr 20, 2008 2:11 pm

### Re: anyone with BP LG book help me out pls?

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Last edited by 062914123 on Mon Jun 30, 2014 3:57 pm, edited 1 time in total.

bp shinners

Posts: 3086
Joined: Wed Mar 16, 2011 7:05 pm

### Re: anyone with BP LG book help me out pls?

flash21 wrote:Pg 289, I'm just wondering why Felicia doesn't have to be included in that chain (in the contra positive) . I still don't understand from the explanation in the book, I've read it over a few times to no avail.

Thank you.

All right, so this one is a little bit tricky.

The original rule is if T, then no F and no V. The rule we are combining it with states if no V then no S. And that's how we get the chain on page 288.

When we take the contrapositive, however, we have to be careful. Any chain with a conjunction (and) or disjunction (or) throws a wrench in the works.

So going back to my original rules, I can see that my contrapositive of the S and V rule is if no S, then no V. That rule doesn't guarantee me anything about F. So we drop F out of the conditional chain. You have to think through this process any time you're making a conditional chain with a conjunction or disjunction.

That is why I usually teach conditional chains with branches. If I have a conjunction as a necessary condition, or a disjunction as a sufficient condition, I will split it into two branches that lead to the same result. So my chain on page 288 would look the same up through T, but then F and V would each get their own arrow. Then, S would follow from the V branch. Then, I could take the contrapositive of the entire changes like that.

flash21

Posts: 1536
Joined: Fri Apr 19, 2013 8:56 pm

### Re: anyone with BP LG book help me out pls?

bp shinners wrote:
flash21 wrote:Pg 289, I'm just wondering why Felicia doesn't have to be included in that chain (in the contra positive) . I still don't understand from the explanation in the book, I've read it over a few times to no avail.

Thank you.

All right, so this one is a little bit tricky.

The original rule is if T, then no F and no V. The rule we are combining it with states if no V then no S. And that's how we get the chain on page 288.

When we take the contrapositive, however, we have to be careful. Any chain with a conjunction (and) or disjunction (or) throws a wrench in the works.

So going back to my original rules, I can see that my contrapositive of the S and V rule is if no S, then no V. That rule doesn't guarantee me anything about F. So we drop F out of the conditional chain. You have to think through this process any time you're making a conditional chain with a conjunction or disjunction.

That is why I usually teach conditional chains with branches. If I have a conjunction as a necessary condition, or a disjunction as a sufficient condition, I will split it into two branches that lead to the same result. So my chain on page 288 would look the same up through T, but then F and V would each get their own arrow. Then, S would follow from the V branch. Then, I could take the contrapositive of the entire changes like that.

Okay thanks - the ands and ors can get a bit messy for sure

bp shinners

Posts: 3086
Joined: Wed Mar 16, 2011 7:05 pm

### Re: anyone with BP LG book help me out pls?

flash21 wrote:Okay thanks - the ands and ors can get a bit messy for sure

Definitely - you have to be really careful with those and/or statements.

Did you check out the video for that game? Sometimes watching the explanation helps a little bit more than reading through the explanation.