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If the first clause depends in some way on the second clause, it acts as an introductory clause and should be separated from the main sentence by a comma

• Example: “In order to irrigate their fields and crops, the ancient Mesopotamian s developed a system of canals.”


So in this sense should a introductory sentence/clause be non-essential in general? What if you should write a complete sentence which introduces instead.


The Mesopotamian' s were very inventive and sought ways to irrigate their fields and crops. They would eventually develop a system of canals for such a task.


Would this example be classified as introductory too.

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panda blue 483So in this sense should a introductory sentence/clause be non-essential in general?

That is not what the guideline is telling you. Commas are not just for non-essentiality; they are used for clarity here.