It is correct to use "then" in a formal sentence?

Here is an example sentence:

"In case that a cylinder is not at end position then the operator has to move manually the cylinder in order to meet this prerequisite"

closed as off-topic by FumbleFingers, Mari-Lou A, Nathaniel, user140086, choster Jan 8 '16 at 2:21

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  • 1
    This is effectively proofreading, so If a cylinder is not at the/an end position then the operator has to move it manually. All the rest is clumsy / ungrammatical / unnecessary verbiage. The word then is also unnecessary, but it's perfectly valid. No-one is likely to think any the less of the writer's competence, whether it's present or not. – FumbleFingers Jan 5 '16 at 12:34
  • As far as I know, using then as the counterpart to if in a sentence effectively structured as "If ... then ..." doesn't raise issues of insufficient formality. Indeed, if the implied "If ... then ..." structure is clear enough (as it is in this sentence), you may choose to omit the then on grounds of its being unnecessary, not on grounds of its being "informal." – Sven Yargs Jan 7 '16 at 7:35
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    Whoever told you to avoid then? Perhaps you or they are misinterpreting other writing advice— not to repeat then in front of multiple sentences in a row, or to be careful about using then when you mean than, for example. All you need to do is read a few technical reports and you will certainly encounter then far more often than ain't or got. – choster Jan 8 '16 at 2:21

It is perfectly acceptable if it's preceded by "if." Like this:

If the cylinder is not at end position then the operator needs to move it manually.

Without "if," your "then" just wouldn't work:

Should the cylinder be anywhere other than the end position, the operator must move it manually.

I hope this helps.

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