The term conditional clause explains itself. Typically, a conditional clause begins with if, when, where, , or because (or one of dozens of similar words) and states a condition that must occur or not occur before something else can occur or not occur, or has already occurred or not occurred, prompting something else to occur or preventing something else from occurring. (I think I said that right.)
Too often we place the conditional clause at the end of a sentence, which prevents us from emphasizing the main point (which is not the condition) and counteracts the natural flow of ideas for our readers.
I'm moving to Borneo, if this Brexit thing happens.
The Portland Commission acts under constitutional authority, when it creates renewal districts.
Adequate notice has been provided where the opponent had a chance to file a written objection.
These sentences make a U-turn at the end, taking our reader back with them and burying the main point. Properly arranged sentences will be chronological: What happens first, goes first. (See Tip: “The Best-Kept Writing Secret of All Time.”) A condition must always happen, or fail to happen, first, so we place it at the beginning of the sentence to set the stage for our main point. That chronological flow helps our readers remember what is important and keeps them moving forward.
If this Brexit thing happens, I'm moving to Borneo.
When it creates renewal districts, the Portland Commission acts under constitutional authority.
Where the opponent had a chance to file a written objection, adequate notice has been provided.
If our sentence contains a condition, it should always come first, even when we simply sign off on an email:
Please let me know if you need further clarification.
If you need further clarification, please let me know.
Hear how much sharper that sounds (on paper)? No reader will sit back and marvel at how well you order your clauses (or avoid passive voice, or use verbs rather than nouns, or remove words with no meaning). They will just love your writing; but they won’t know why.