Formal logic can also be used as a basic framework that can then be enriched with signs that denote “X is permitted” and “X is obligitory”. All such deontic logics need “ought” in the premise to get to “ought” in the conclusion.

http://plato.stanford.edu/entries/logic-deontic/

The unspoken deontic premise in Ethical Inference is something like

Agents ought to take actions that will lead to desired outcomes.

My objections to this premise are many. Here’s just three:

Perhaps no action is required.
Perhaps there’s an easier way to achieve the same goal
Perhaps what the agent (e.g. Hitler) wants is bad and wrong

[Your example reminds me of the Wim Wenders movie Wings of Desire, in which a disembodied and immortal angel wants to become human in order to experience things that it cannot in its angelic state. For such an angel (if its name were "Lassie") your example would indeed have recommendatory force.]

In your second example of inference, using a sledgehammer to kill a fly, the first premise, while true, is not very workable, as you note. The strength of the recommendation is weak because of the weakness of the first premise.

Just as a logical argument can be valid in form but lead to a false conclusion if one or more premises are false, an ethical argument can be valid in form but lead to a foolish conclusion if one or more of its premises are unsuitable or inappropriate.

You say

Ethical Inference looks … weak to me, since it ignores the fact that there can be many means to a given end.

The ethical inference does not have the force of formal logic. It does not provide deductive certainty. But it does have practical import and is a useful way of reasoning, particularly if you evaluate thoughtfully the premises.

1) If a being is a human, then that being is mortal
2) Lassie wants to mortal (let’s just suppose)
3) Therefore, Lassie ought to be human (huh? why would this follow?)

This is quite silly. Lassie is under no obligation to be human, regardless of what Lassie wants in terms of mortality. Lassie has already achieved the supposedly desired state of mortality in a different way – by being a dog.

This points to a systematic problem in the form of argument you’ve labeled Ethical Inference. Let’s try another example of the same form.

1) If I hit a fly with a sledgehammer, it will die
2) I want to kill this fly
3) Therefore, I ought to hit it with a sledgehammer

Well … there are easier ways to achieve the same goal. Ethical Inference looks very, very weak to me, since it ignores the fact that there can be many means to a given end.

I can see where the accusation of affirming the consequent comes from. Affirming the consequent tries to go backwards, from the consequent of an if – then to the antecedent, ignoring the fact that there can be many reasons why a given consequent is true.

Syllogisms are neither true nor false. Truth and falsity apply to the premises and conclusion, not to the syllogism as a whole. The syllogism as a whole is either valid or invalid. So the question “Would this syllogism be true?” is not meaningful.

My ethical inference is not Modus Ponens. It is based on Modus Ponens, but it is not the same. Please see my newer post on the subject here:
http://www.bmeacham.com/blog/?p=966

In any case, no matter how much of slob or homely Mary is, she will have a better chance of getting along with others if she is honest and friendly than if she is a liar and hostile.

Thanks for the reply. I am aware the Modus Tollens reveals the conclusion as false. That was actually the point I was trying to make.

The example you use was Modus Ponens.
You used this as an example:
If [P] you want to get along with people, then [Q] you ought to be honest and friendly.

We can spell this out logically as follows:

Premise: People who are honest and friendly get along with other people.
Premise: You want to get along with other people.
Conclusion: You ought to be honest and friendly.

What I was trying to show was that through Modus Tollens, the example doesn’t hold up as you point out.

> Would this syllogism be true?:
Premise: People who are honest and friendly get along with other people
Premise: Mary doesn’t get along with others
Conclusion: Mary is not honest or friendly with others.

“No. That is a fallacy called Denying the Antecedent. Maybe Mary gets along with others even though she is not honest and friendly. Maybe she is rich, and people hang out with her even though they don’t like her personality.”

I agree with you that when we apply modus tollens the syllogism reveals a fallacy. Mary may be the victim of prejudice. Maybe she’s obese or homely or aside from being honest and friendly, she’s a bit of a slob. Being honest and friendly doesn’t guarantee that she gets along with others. So I guess my question is, how does the use of modus polens show that ought is derived from is when modus tollens shows that as a fallacy?

I think the point is that in any deductive syllogism, IF the premises are true, THEN the conclusion MUST follow. In my example the conclusion doesn’t follow because one or more of the premises hasn’t been demonstrated as true.

‘If you want to get along with people, it is helpful to be honest and friendly’ is more rational, ie, you could take a survey and find out.

Check out Albert Ellis on the matter.

No. That is a fallacy called Denying the Antecedent. Maybe Mary gets along with others even though she is not honest and friendly. Maybe she is rich, and people hang out with her even though they don’t like her personality.

> Would this syllogism be true?:
> Premise: People who are honest and friendly get along with other people
> Premise: Mary doesn’t get along with others
> Conclusion: Mary is not honest or friendly with others.

That is a valid argument. In fact, it is Modus Tollens. It is valid because it is not possible for the premises to be true and the conclusion to be false.

> we don’t have firm refutation of Kant’s Moral Law.

Right. I am not attempting to refute Kant in this essay.