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Examples:

  • If you lie, then you're out.

  • If you do it right, then you can have a cookie.

The above are standard if/then clauses. "If" is a subordinating conjunction introducing a subordinate clause, so it is separated from the main clause, the "then" clause, by an ensuing comma. Now I know that if you leave the "then" implied, that you still use a comma.

Examples:

  • If you lie, you're out.

  • If you do it right, you can have a cookie.

HOWEVER, it has become common to leave the "if" implied as well, but how do you punctuate it?

Examples:

  • You lie, you're out. --or-- You lie; you're out.
  • You do it right, you can have a cookie. --or-- You do it right; you can have a cookie.

Part of me thinks that a comma is necessary because the first clause is still subordinate with or without the subordinating conjunction "if." But then another part of me thinks that lacking an explicit "if," it isn't actually a subordinate clause, so the two clauses become interdependent, so a semicolon instead of a comma is called for.

Here's why I think that:

  • I like it, but I don't love it.

When we use a conjunction to introduce an additional clause, we separate them with a comma. However, when we omit the conjunction but leave the conjunction implied, we can no longer grammatically use a comma to separate the clauses but must instead use a semicolon.

  • I like it; I don't love it.

So following that line of thinking, maybe a semicolon is required in the examples above.

I have searched the internet for how to punctuate if/then sentences when both the "if" and the "then" are implied, but I have not been able to find anything on the subject. All I can find are grammatical explanations for omitting the "then," not the "if" too.

Any light you shed would be greatly appreciated.

  • 2
    You might like to read the answer at the “If” with implicit “then” question: Should a comma be used? thread to de-prescriptivise your first two claims. // The recent acceptability of the modern staccato version probably licenses any sensible punctuation in informal contexts. I'd use 'You lie – you're out.' but 'You do it right, you can have a cookie.' And either 'I like it – I don't love it.' or 'I like it, I don't love it.' or 'I like it; I don't love it.'. – Edwin Ashworth Feb 15 '17 at 22:37
  • Thanks, Ed. I read that link. I don't agree with it. Everything I've ever read—a mountain of sources—indicates the opposite, indicates that a comma is required. Whenever a subordinate clause appears before a main clause, it is ALWAYS followed by a comma. The subordinating conjunction "if" makes the clause a subordinate clause. Whether or not "then" appears, the ensuing clause is still a main clause. Not having "then" doesn't make it not a main clause. So despite the many upvotes that answer got, it's nonetheless wrong. But thanks for your interest in the question. – Benjamin Harman Feb 15 '17 at 22:44
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    There is a mixture of examples including the comma and ones omitting it on the first page of a Google search for "When he had gone I". Modern usage prioritises first clarity/disambiguation, then indication of intended pauses in reading, before slavish adherence to 'rules'. // The occasional acceptability of the comma splice (even its preference over a semicolon in rare cases) has been covered here before. – Edwin Ashworth Feb 15 '17 at 23:01
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You could use a colon to separate the two short sentences, because you are stating the antecedent and then the logical conclusion of an implied if..then rule, completing a "Hypothetical syllogism" by affirming the consequent having posited the precedent.

This would be a use of the "syntactical-deductive" use of a colon to introduce the logical conclusion of the fact stated before the colon. To me, in written English the colon makes it more clear that you are making a conclusion based on an implied If..Then rule.

The implied if..then rule is the major premise, called a "conditional proposition" that is a statement that has an antecedent and a consequent. (If [antecedent] then [consequent]). The minor premise is a categorical proposition affirming the antecedent. By "modus ponens", the consequent is a logical conclusion of the antecedent. "You lie: you're out." The three statements form a "hypothetical syllogism".

You could also reverse the negatives of the sentence, as in "You're not You could also reverse the negatives of the sentence, as in "You're not out: you didn't lie", by "modus tollens".

For the other example "I like it: I don't love it", there isn't a clear implied If..then rule. The syllogism would be an example of a disjunctive syllogism, where the major premise is a disjunctive proposition stating disjointed alternatives and the minor premise is a categorical proposition about one of the alternatives. This gets shaky when the alternatives are not mutually exclusive: you don't have a true disjunctive proposition. A person could both like something and love the same thing. Therefore stating or denying one of the alternatives doesn't have a true conclusion. The two statements are independent and should have a semicolon. "I like it; I don't love it." (two independent facts). "I don't love it: so I don't like it" does not make sense because to most people it is not a true categorical proposition that "You can either like something or love it".

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I like it— I don't love it.

You lie — you're out.
The Punctuation Guide

I prefer the "em" dash for the described examples.
The examples probably should not be used in formal writing, except to report what somebody has said, or when attempting to get the reader's attention.

The above cite from The Punctuation Guide does not allow for the use of a "em dash" to replace a semi-colon. Generally it can replace parentheses:

I like it (I don't love it).

You lie (you're out).

That works for the first example, not the second.
I am stuck on the "em" dash.

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