PHIL 410A: HANDOUT ON REASONING

IMPORTANT TERMS AND ABBREVIATIONS

 

I assume that students taking a 400-level level philosophy course are familiar with basic logical terminology. Items 1-7 on this handout provide a summary of the necessary terminology. Items 8-11 use that terminology to make some distinctions that will be important in this course.

 

1. Properties [Terms] and Propositions [Sentences]. Capital letters, "A", "B", "P", "Q", etc. can stand for properties [expressed by terms, such as "is morally justified"] and propositions [expressed by sentences, such as "Governments ought to guarantee a protected sphere of liberty."]. Small letters ("p", "q", etc.) can also be used to stand for propositions.

 

Complex properties and complex propositions can be constructed out of simpler ones by the following logical operations:

(a). Negation. The negation of male (M) is not male (-M).

(b) Conjunction. The conjunction of brother (B) and father (F) is brother and father (B&F).

(c) Alternation. The alternation of brother (B) and father (F) is brother or father (BvF). A person is a BvF if he is a B or if he is a F or if he is a B and a F.

(d) A conditional is a proposition of the form: If P, then Q.

 

2. Metaphysically Necessary And Metaphysically Contingent Truths and Falsehoods. If a proposition is such that it could not be false, then the proposition is a metaphysically necessary truth. If it is the negation of a metaphysically necessary truth, it is a metaphysically necessary falsehood. In this course, whenever we use the term "necessary" without modification, it will be assumed that we are speaking of metaphysical necessity. If a proposition is neither necessarily true nor necessarily false, then it is contingent (either contingently true or contingently false).

 

3. Implication and Necessary Equivalence. I say that one property [or proposition] P implies another property [or proposition] Q [P Q], just in case: (a) [for properties] it is not possible for something to have property P without having property Q; or (b) [for propositions] it is not possible for P to be true unless Q is also true (i.e., it is not possible that P & -Q). For example, the proposition that I am a father implies the proposition that I am male, because the property of being a father implies the property of being male [Father Male]. To say that P Q is to say that the conditional [If P, then Q] is necessarily true.

I will say that one property [or proposition] P is necessarily equivalent to another property [or proposition] Q, just in case P Q and Q P, which is abbreviated P Q. Explain why being a father is not necessarily equivalent to being a male.

 

4. Counterexamples. The usual strategy for attempting to show a conditional to be false it so provide a counterexample to it. To find a counterexample to [If Male, then Father] it suffices to show that there is something that is a male but not a father. You should easily be able to think of someone who is a counterexample to [If Male, then Father]. In general, a counterexample to a conditional [If P, then Q] is something that exists that is P but not Q. Philosophers spend a lot of time attempting to construct counterexamples to claims of implication. To construct a counterexample to the claim of implication P Q, it is not necessary to show that there actually exists something that is P but not Q. It is enough to show that it is possible that there be something that is P but not Q. Thus, for example, even if all crows that ever exist are black, if it is possible for there to be an albino crow, then being a crow would not imply being black.

 

5. [Metaphysically] Necessary/Sufficient Conditions.

 

(a) Sufficient Condition. A property [or proposition] P is a [metaphysically] sufficient condition for a property [or proposition] Q, just in case P implies Q--that is, P  Q. Thus, for example, being a father is a sufficient condition for being male, because Father Male.

 

(b) Necessary Condition. A property [or proposition] Q is a [metaphysically] necessary condition for a property [or proposition] P, just in case P implies Q--that is, P Q. For example, being male is necessary for being a father. [An equivalent way of thinking of a necessary condition is the following: If Q is necessary for P, then the negation of Q implies the negation of P--that is, ‑Q ‑P (e.g., Because anything that is not male is not a father, being male is a necessary condition for being a father).] Note that if P is sufficient for Q, then Q is necessary for P.

 

(c) Necessary and Sufficient Condition. A property [or proposition] P is a [metaphysically] necessary and sufficient condition for a property [or proposition] Q, just in case P and Q are necessarily equivalent (i.e., P Q). For example, having 5 things is necessary and sufficient for having 12-7 things.

 

6. Definitions. A definition of a term T states its meaning in more basic terms. Example: sister =df female sibling. An acceptable definition of a term T provides necessary and sufficient conditions for T. But not every necessary and sufficient condition for a term T provides a definition of T. Use the example of 5 = 12-7 to explain why not.

 

7. Deductive Implication. Suppose you are given a set of premises and a conclusion. Whenever the logical form of the premises and the conclusion is such that it is not possible for the premises all to be true and the conclusion to be false, we will say that the premises deductively imply the conclusion. Whenever a group of premises deductively imply a given conclusion, we will say that the combination of premises and conclusion is a valid deduction. Here is an example of a valid deduction:

 

PREMISES: MP1. It is always wrong to kill another person. (This is a Moral Principle)

P2. I am a person.

P3. If you shoot me, I will die.

CONCLUSION: PMJ1. It is wrong for you to shoot me now (This is a Particular Moral Judgment).

 

8. Top-Down Reasoning: Begins with moral principles and other acceptable premises and uses them to support a moral judgment about a particular actual or hypothetical case (a particular moral judgment).

 

9. Bottom-Up Reasoning: Begins with judgments about particular actual and hypothetical cases and uses them to support the moral principles that best explain those particular moral judgments. Bottom-Up reasoning supports moral principles that explain our particular moral judgments and undermines moral principles that do not. So moral principles are never regarded as infallible.

Here is an example of how Bottom-Up Reasoning can lead one to give up a moral principle:

 

PREMISES: MP1. It is always wrong to kill another person. (Moral Principle)

P2. I am a person.

P3. If you shoot me, I will die.

P4. I am trying to kill you.

CONCLUSION: PMJ2. It is wrong for you to shoot me now (even though I am trying to kill you).

 

Let PMJ2' be the judgment that it is not wrong for you to shoot me now if I am trying to kill you. If you accept PMJ2', you must reject one of the premises of the above valid deduction. The premise that seems to need revision is the moral principle MP1.

 

10. The Proof Paradigm. For most of its history, Western philosophy has assumed that reasoning fits the Proof Paradigm. On the Proof Paradigm, we must have an infallible source of knowledge of the fundamental moral principles (e.g., God, our Reason, etc.). Then reasoning about particular cases is Top-Down, from moral principles to particular moral judgments.

 

11. Equilibrium Model of Reasoning. Equilibrium Reasoning is both Top-Down and Bottom-Up. In Equilibrium Reasoning, our main reason for accepting a moral principle is usually that it seems to provide a good explanation of particular cases. When we accept a moral principle on this basis, we can then reason Top-Down from that moral principle to a particular moral judgment, but the moral principle is not regarded as infallible. If we discover a particular moral judgment that the principle conflicts with, we must either give up the particular moral judgment or give up the principle. The decision about which to give up is based on what makes the most sense.

In this course we don't prove anything. We use equilibrium reasoning to try to find principles that explain our judgments about particular actual and hypothetical cases. When someone proposes such a principle, we consider its deductive implications and try to find counterexamples to it. If we decide that there is a counterexample to a proposed principle, we don't give up trying to find an adequate principle. We use counterexamples as clues to help us formulate better explanatory principles.

 

The U.S. Declaration of Independence shows the influence of the Proof Paradigm in political philosophy. (Can you explain why?) By the end of this course you should be able to explain why the U.S. Constitution represents giving up the Proof Paradigm and moving to the Equilibrium Model of moral reasoning for political philosophy.