Some grammatical rules and errrorrs in writing essays:
In summaries, keep to one tense. If you were to switch, it was confusing.
Subjects and verbs should agree; when it don't, they are in error.
Sentence fragments are. Being incomplete.
Comma splices connect independent clauses, they do so with a comma, however,
this is inadequate adhesive for such independent elements. Use a semicolon; use a
A run-on sentence blurs thoughts together like a comma splice without the comma
it does not separate independent clauses.