Since "if P, Q" is grammatical, is it not the case that the "then" in "if P, then Q" is redundant?

Where P and Q are clauses.

For example, "if it rains today, the road shall be wet tomorrow" is grammatically impeccable. (Or is it not?)

Doesn't that mean that the "then" in "if it rains today, then the road shall be wet tomorrow" is redundant? I am referring to the logic that using a word would be redundant if the same meaning is conveyed without that word.

But I see that, when the antecedent clause gets too long, the occurrence of "then" serves to mark the distinction between the two clauses.

Except in that sense, can we not say that the usage "if ... then" is redundant in English, and should be replaced by "if ..." especially if the clauses are short enough?

Ah, except in programming languages, of course.

  • Can you give us an example to help clarify? – Nicole Apr 21 '15 at 23:56
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    I've been working in DEC/Alpha Basic so long [since 1988 - I said I was old-school] that I think I tend to overuse 'then' when speaking normal English. But I agree that it's a good idea to use 'then' unless it's a simple sentence where the start of the consequence is obvious. – David Garner Apr 22 '15 at 13:23
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    I'd not use a 'then' is such cases (but as you wisely point out, it might be useful with a long antecedent). But redundancy is largely a matter of style rather than of absolute correctness / incorrectness. And 'This room is spic' is incorrect. – Edwin Ashworth Apr 26 '15 at 23:32
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    The Phrase Finder has for spick and span 'The alliteration in the phrase suggests the possibility that that one of the two words alluded to cleanliness and freshness and that the other just followed along.' (ie one's just there for prosodic effect, as with a 'goody-goody'. It's redundant: it contributes nothing to the meaning.) But spic/spick (or span) on its own is unacceptable. (... The use of spic ... is just an alternative spelling of spick.) – Edwin Ashworth Apr 27 '15 at 22:14
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    As a mathematician, I frequently write such conditional statements. My advice: include the "then" unless perhaps the antecedent is extremely short. Help the reader keep track. – GEdgar Oct 22 '15 at 15:59

I would not consider it redundant to have if...then...

Leaving aside the point of using then to clearly mark where the consequent clause begins, the use of both if and then can serve to emphasize the causal nature of the antecedent, or to make it seem like an if and only if rather than just an if-then.

For example:

If it rains, we will stay inside.

merely provides the plan of action in the case that it rains, whereas:

If it rains, then we will stay inside.

seems to suggest that the staying inside will only happen if it rains (note the emphasis on then, which would be stressed in speech and italicized in writing).

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    bcc32's logic is fallacious. "If it rains, then we will stay inside" means that we will definitely stay inside if it rains, but rain is not a requirement for staying inside. – user143926 Oct 22 '15 at 15:53
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    That’s what “If it rains, we’ll stay inside” means. If you add and stress then, the meaning does it fact come closer to meaning “We will only stay inside if it rains, otherwise we will [do whatever it we’re doing] outside” as bcc32 says. This is contingent upon actually stressing the then, though, which bcc32’s answer does not mention except for italicising the word. – Janus Bahs Jacquet Oct 22 '15 at 16:21
  • The meaning is only changed if "then" is emphasized. – Hot Licks Oct 22 '15 at 17:56
  • Edited for clarity. – bcc32 Oct 25 '15 at 21:10

"If X, then Y" is ordinary English usage and, although slightly redundant, is unobjectionable. Two related points: (a) "If and only if X" ("iff"), beloved of philosophers, seems to me redundant for "Only if X", as well as being awkward to speak or write - or am I missing something? (b) Too often, I encounter "If then, ..." or "If, then, ... ." I know of no excuse for these. They seem to be awkward and confusing substitutions for "Then, if... ."

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    Nope. Only if is quite different from if and only if -- there is nothing redundant about the latter. P only if Q is typically translated in logic as Q implies P, not P is equivalent to Q (aka P if and only if Q, aka P implies Q and Q implies P). P only if Q is false only when Q is true and P is false. (This is the conventional interpretation for logic, but there are of course other interpretations. English is a natural language.) – Drew Oct 24 '15 at 20:37

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