Philosophy of Computer Science: Online Resources

Position Paper #3:

Is the Brain a Computer?

Assignment

The Argument

1. Turing's Thesis: A physical object can compute if and only if it can do what a (Universal) Turing Machine can do.

2. A computer is any physical device that can compute.
   (Consider this as a (proposed) definition of 'computer'.)

3. The human brain is a physical object that can do what a (Universal) Turing Machine can do.

4. Therefore, the human brain is a computer.

5. Microsoft Word is Turing Machine-computable.
   (That is, a Universal Turing Machine can execute Microsoft Word.)

6. Therefore, any computer can execute Microsoft Word.

7. Therefore, the human brain can execute Microsoft Word.

• If both of those conditions hold, then the argument is sound.
• You are logically obligated to believe the conclusions of sound arguments!
  • So, if you ever come across an argument that you think is sound, but whose conclusion you don't believe
    (by the way, do you really believe line 7 of this argument?),

    then either one or more of the premises are false or it is invalid (that is, there is some way for the premises to be true yet for the conclusion to be false).

1. To determine whether the argument is valid, you must suppose (or make believe) "for the sake of the argument" that all the premises are true, and then consider whether the conclusions logically follow from them. (Or: Can you imagine some way the world might be so that the premises are true but the conclusion is false?)
   • Note that there are three conclusions: line 4, line 6, and line 7. So, do you agree that line 4 follows logically from premise 1–premise 3, and/or that line 4 follows logically from premise 5 (maybe with the help of some of the earlier premises), and/or that conclusion 7 follows logically from line 4 and line 6 considered as premises?

     If not, are there missing premises that are needed to make the argument(s) valid? If there are, do you agree with them (why/why not)?

2. It may be too difficult to determine whether each premise is true or false. More realistically, you should decide whether you believe, or agree with, each premise, and you must explain why you do or don't.

Finally, do you agree with the conclusion(s)? If you do, but you think that there's something wrong with the argument, try to present a better one. If you don't agree with the conclusion(s), state why, and try to give an argument for what you do believe.

Ground Rules

1. Please bring 5 copies to lecture on the due date.

2. At the top of the first page, please put the following information:
   1. the title "Position Paper #3"
   2. your name
   3. the course you are enrolled in
   4. the due date.

3. For general assistance with writing (including a suggested method of paper preparation and format, as well as advice on grammar), see my website "How to Write". As before, no abstract is needed for this position paper, but you do need to give full citations to any sources that you cite.

Suggestions and Guidelines for Peer-Group Editing

1. When you get into your small groups, introduce yourselves quickly, and share copies of your papers with each other.

2. Choose one paper to discuss first.
   (Suggestion: Go in alphabetical order by family name.)

3. After spending about 10–15 minutes on the first paper, move on to the next, going back to step 2, above, changing roles. Spend no more than 15 minutes per paper (because you've only got about 45 minutes at most). Perhaps one member of the group can be a timekeeper.

4. For each paper, ask as many of the following questions as you have time for:
   1. Did the author state whether the argument from premise 1–premise 3 to conclusion 4 was valid?
      1. If they thought it was invalid, did they suggest a missing premise that would make it valid (if that's possible)?

   2. Did the author state whether the argument to conclusion 6 was valid?
      1. Did they correctly identify its other premises besides premise 5?
         (Very few real arguments can have only one premise.)

      2. If they thought it was invalid, did they suggest a missing premise that would make it valid (if possible)?

   3. Did the author state whether the argument to conclusion 7 was valid?
      1. Did they correctly identify its other premises besides premise 6?
         (Note that sentence 6 is both the conclusion of the previous argument and a premise of this one.)

      2. If they thought it was invalid, did they suggest a missing premise that would make it valid (if possible)?

   4. For each premise, ask whether the author stated whether and why they did or did not agree with it.
      1. If the author agreed, then it is preferable (but not necessary) that they give reasons for agreeing. If they did give such reasons, do you agree with those reasons? Why?

      2. If the author disagreed, then it is necessary that they give reasons for disagreeing, so do you agree with those reasons? Why?

   5. For each argument, if the author thought it was unsound, did they state whether they believed its conclusion anyway, on independent grounds (that is, for different reasons)?
      • And, if so, do you agree with those reasons?

5. Keep a written record of the questions and replies. This will be useful to the author, for revision.

6. At home, over the next week, please revise your paper to take into consideration the comments made by your fellow students (that is, your "peers"): Perhaps defend your claims better, or clarify statements that were misunderstood, etc. For help, see your instructor.