April 20, 2014

Homework Help: Logic

Posted by Tom on Wednesday, November 5, 2008 at 4:44pm.

I know this is alot of text, but i'm having trouble understanding what my professor is asking...

Study questions and Homework: St. Thomas Aquinas' arguments for the existence of God.

Reading and Homework due: November 6, 2008.

Work through the following, to see if you understand every step. Whenever an inference is made you will see the lines used as premises surrounded by “{ }”; you should be able to name the argument form that is used to make the inference.

Palmer quotes the third of Thomas’s five ways (to reason our way) to the existence of God.

In the world of sensible things we find there is an order of efficient causes. There is no case known (neither is it, indeed; possible) in which a thing is found to be the efficient cause of itself; for so it would be prior to itself, which is impossible. Now in efficient causes it is not possible to go on to infinity…. Now to take away the cause is to take away the effect. Therefore, if there be no first cause among efficient causes, there will be no ultimate, nor any intermediate causes…. Therefore, it is necessary to admit a first efficient cause, to which everyone gives the name of God.

Thomas is trying to argue to the conclusion: God exists. Construct the argument from the above. You cannot do this mechanically. You have to think about what he is really trying to say. Here are the constraints on your task:
a. the conclusion is “God exists.”
b. your construction must be based on Aquinas’s words. You can paraphrase; but you have to be able to defend your paraphrase.
c. Aquinas is neither a fool nor a knave, which means your construction must be charitable, making the best argument one can, given Aquinas’s actual words.

How about this as a construction?

1. Every thing is caused.
2. If every thing is caused, then it is caused by itself or by something else.
3. Nothing causes itself.
{1,2} 4. Thus, every thing either causes itself or is caused by something else.
{3,4} 5. Thus, everything is caused by something else.

Thomas apparently thinks that premise 3 needs an argument because he gives us one:

1.’ If a thing caused itself then it would exist prior to itself.
2.’ Nothing exists prior to itself.
3. Thus nothing causes itself.

Now given the conclusion in line 5, Aquinas seems to want to assure us that that no sequence of causes can go on to infinity. He asserts “Now in efficient causes it is not possible to go on to infinity.” He argues for this claim this way it seems:

6. If everything is caused by something else then every chain of causes is infinite.
7. If every chain of causes were infinite then there would be no beginning to any chain of causes.
8. If there were no beginning to any chain of causes then there would be no effects.
9. But there are effects.
{8,9} 10. Thus, it is false that there is no beginning to any chain of causes.
{10, 7} 11. Therefore, it is false that every chain of causes is infinite. I.e. there is a chain of causes that is not infinite. [While this is weaker than the claim than there is no infinite chain of causes, it is strong enough for Aquinas to get the conclusion for which he is aiming.]

Having, 11, Aquinas proceeds:

{11, 6} 12. Therefore, it is not the case that everything is caused by something else. I.e there is something that causes itself.
13. If something causes itself then there is an uncaused cause.
{12, 13} 14. Thus, there is an uncaused cause.
15 An uncaused cause is called God.
16. Thus God exists.

Homework: Turn in answers to the following two questions.

1. Have we observed our three constraints? Note the argument is valid. Is it sound?

2. Look at the premise, line 1 and the conclusion, line 14. How can both of these be true? What conclusion must we draw?

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