Logic: The 'is-ought' problem

A seemingly simple question:
Can we infer an ought statement from an is statement?

And one example of such derivation was given by amiya :

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EXAMPLE
Premises: 1. John eats chocolates.
2. John does what he ought to do.

Conclusion: Therefore John ought to eat chocolates.

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Neat indeed!
I appreciate the way the above example has been constructed.

However, if inference is being used in this question as in logic, then one should first state what logic is being used, what an is-statement is and what an ought-statement is.

First order logic, for example, does not have anything to do with the structure of statements except those introduced by its own connectives, quantifiers, inference rules etc.

Therefore, the discussion will not be meaningful until the terms involved in the question are defined. Or, at least, explained with some clarity.

Now, I will myself jump the gun. That is, I will add to this discussion without myself attempting what I have asked for (the definitions).

An ought-statement cannot be inferred unless there is an ought within the premises or in the rules of inference. This is, of course, obvious. Because, if the ought-clause is already there in a complex proposition, it may be possible to infer it in a valid way. But, if the premises do not contain either an implicit or an explicit ought-clause, there has to be a rule of inference that allows ought to be inferred from is.

Also, ought is about an imperative and is applicable where, seemingly, the opposite of what has been asserted as an ought is a likely course of action. On the face of it, a choice among various course of actions can be justified by inference only if the consequences or the circumstances related to choices can be arranged in some order of preference. This ordering is then a premise in our argument, and the inference would require, in addition to the aforesaid premise, another premise of the form: "The choice of action ought to be in accord with the most preferred item in the ordering (mentioned above)."

Or this last statement will be a rule of inferring the choice of action. But with this rule, we have a new species of logic. On this, I will say nothing further.

But, in ordinary english, let us be clear that the justification of a choice of action from is-statements has more to do with rationality than logic.

Inferences as to what a rational person would under the given is-premises itself involves a lot many unstated assumptions which implicitly depend upon some mutually agreed upon ordering of the kind mentioned above.