"Otherwise" is listed as a conjunctive adverb. That is the reason for the comma.
Student or Learner
otherwise [sentence adverb]: used when saying what bad thing will happen if something is not done:
- You'll have to go now, otherwise you'll miss your bus.
- Put your coat on, otherwise you'll get cold.
I'd like to ask why a comma is used before 'otherwise' in each sentence above. Why not a semicolon?
''A semicolon joins two clauses when the second includes a conjunctive adverb such as accordingly, however, indeed, or thus, or a phrase that acts like a conjunctive adverb such as in that case, as a result, or on the other hand'' (page 32).
The source: Merriam-Webster's Manual for Writers and Editors by Merriam-Webster.
I feel a little confused. You say that "otherwise" is listed as a conjunctive adverb. That is the reason for the comma.'' but in the book it is the opposite.