HOW TO USE THEN
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THEN can be used as an adverb, a noun, and an adjective. However, it is not a conjunction.

THEN can be used as an adverb to indicate an order of time or part of a list. Examples:

The dragon circled the sheep herd and then dove.

The dragon swallowed a sheep then belched.

THEN can be used as a noun. Example:

Since then, the dragon kept a close eye on the sheep.

THEN can be used an adjective. Example:

The then head dragon watched the herd of sheep.

Read about CONJUNCTIONS