Considering the presupposition that there are objective answers to prescriptions, are prescriptions truth-apt? My definition of a prescription is that it is simply an conditional.


You ought to take the flight to arrive at location B from A the fastest.

We can convert this to a conditional of the form P⊃Q where P is "you want to arrive at location B from A fastest" and Q is "take the flight". Let's say that it is objectively true that taking a flight would be the fastest way for all possible states.

Is this statement truth-apt? Isn't truth aptness the capacity of a statement to be true. Does it make any sense to say it is truth-apt if the result is a command (which is not truth-apt) instead of a proposition. And yet according to wikipedia it is apparently controversial. What have I missed?

  • 2
    No, not exactly. "If you want to get from A to B the fastest then you ought to take this flight". Neither your P nor Q are declaratives, or truth apt, as in a conditional, and hence "if P then Q" is not truth apt in the usual sense either. There are logics of imperatives that validate some conditionals containing imperatives (If you ought to do this then you ought to do that). But these are not themselves imperatives ("prescriptions"), but rather declaratives about imperatives (facts about prescriptions), see deontic logic.
    – Conifold
    Dec 1, 2018 at 5:24
  • @daegontaven. 'arrive ... the fastest'. Arrival marks the end of a process (here a journey) and is durationless. It can take me two hours to journey - travel - from B to A; it takes no time to arrive. Arrival simply signifies that the journey has ended.
    – Geoffrey Thomas
    Dec 1, 2018 at 9:22
  • @Conifold Thank you for pointing that out. I had a different understanding of truth-aptness at the time of writing. Now I understand context matters. So I've reworded P to match the requirements. Would P now be truth-apt? I see what you mean by declarative. Perhaps I would argue that imperatives are simply conditionals pertaining to agents in a system. Dec 1, 2018 at 16:43
  • @Conifold assumes all conditionals are equally valid which is fallacious thinking. Necessary and impossible conditionals exist which necessitate some conditionals and invalidate others, respectively. Dec 2, 2018 at 0:34

1 Answer 1


I don't think this is best taken as a stand-alone question. Different assumptions can lie behind it.

Practical 'oughts' and truth-aptness

'You ought to take this flight' might be a truncated hypothetical. If (a) we complete it with, 'You ought to take this flight if you want to get the fastest from B to A' and (b) it is true that you do want to get the fastest from B to A, and (c) the 'ought' here is not moral but practical or 'technical' or predictive, it can perfectly well be true that you ought to take this advice. It simply contains a practical truth.

Moral 'oughts' : fact/ value versus is/ ought

When 'ought' has a moral dimension, to indicate what you have a moral duty or obligation to do, matters become more complex.

Suppose the fact/ value distinction is bogus : suppose it is a fact that justice is a good and so is honesty and so is gratitude and so is benevolence and so on and on. Suppose e.g. 'justice is a good' (an evaluation or evaluational statement) has truth-conditions which are satisfied.

Situational moral truth-aptness

The moral prescription (or prescriptive statement) would not follow that you (morally) *ought' to act justly in a particular situation. Evaluations do not yield prescriptions. This is because (for one reason) there is a plurality of moral values, not all of which are compossible in particular situations and which cannot be lexically ordered. More simply : there is no guarantee that specific values will not situationally clash and there is no plausible way of ordering the different moral values in order of priority. We cannot say that justice always is morally more important than gratitude, or gratitude always less important than benevolence. Moral values, with apologies to Plato, are rivalrous in particular situations for action.

So even if it is true that justice is a good, the corresponding moral prescription does not follow that you ought to act justly in such-and-such a situation; benevolence might have situational priority.

Now, whether situational prescriptions, e.g. 'In this situation you ought to act benevolently rather than justly', are truth-apt. is not at all clear to me. All I can say is that if the fact/ value distinction is bogus, and there can be moral facts such as 'justice is good', I can see no reason in principle why situational prescriptions ('you ought to act justly in this situation') cannot be truth-apt too. All I have stressed is that there is no straight implication from 'justice is good' to 'you ought to act justly in this situation'.

'But how can prescriptions be truth-apt if they are commands ? Doesn't your argument break down at and on this point ?' Not at all.

Prescriptions are not commands

I quite see that commands are not truth-apt but 'you ought to act justly in this situation' is not a command. 'You ought to act justly in this situation' is a prescription, a statement about what you ought to do, and nothing like what it would have to be if it were a command such as 'Act justly !'

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