Front Page Titles (by Subject) Is/Ought and Probable Reasons - Literature of Liberty, October/December 1978, vol. 1, No. 4
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Is/Ought and Probable Reasons - Leonard P. Liggio, Literature of Liberty, October/December 1978, vol. 1, No. 4 
Literature of Liberty: A Review of Contemporary Liberal Thought was published first by the Cato Institute (1978-1979) and later by the Institute for Humane Studies (1980-1982) under the editorial direction of Leonard P. Liggio.
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Is/Ought and Probable Reasons
“A Grammatical Point about Obligation.” Philosophical Quarterly (Scotland), 28 (July 1978): 229–233.
The is/ought problem may dissolve by exploiting a well-known point in probability theory. Consider how the following argument operates: “I have two pairs, so there is a probability of about 1/10 that I'll make a full house.” The probability evaluation is not part of the conclusion; rather, it reflects the strength of the connections between the premise and the conclusion. In other words, from the premise (“I have two pairs”), the conclusion (“I shall get a full house”) follows in the sense that it has a certain probability of following.
The same move holds for the is/ought question. The “ought” does not lie in the conclusion but rather in the connective. Accordingly, we commit no fallacy by moving from “is” to “ought” since our argument does not proceed in that fashion. For example, consider another argument: “You received some oranges from the grocer, so you ought to pay him for them.” This argument does not say that from the fact of your receiving some oranges the normative statement (“You ought to pay”) follows. It actually says that from the fact that you received the oranges, the fact of paying the grocer ought to follow. This claims that we ought to be able to pass from one statement of fact to the other statement of fact.
Besides striving to dissolve the is/ought problem, this approach may be an improvement for two reasons. First, it clarifies the notion of a reason for action. Consider the inference: “If I did p, therefore I ought to do q.” It is puzzling how my merely doing p can move me (or put me under an obligation) to do q. A way out of this non sequitur exists if the previous inference means that doing p gives me a reason to do q (that is, one ought to pass to the fact of doing q), then we can investigate how reasons motivate us. Second, this approach resolves differences between deontologists who build their ethics upon “right,” “ought,” and “duty,” on the one hand and teleologists who build their ethics upon “good” or “pleasure.” Since “evaluative” terms simply measure the strength of moving from premises to conclusions in a moral argument, we can accept both sorts of moralists' terms depending on the case involved. Which ethical approach is acceptable depends on how strong is the connection between premise(s) and conclusion.