When you connect two complete sentences (a.k.a. independent clauses) with a coordinating conjunction (for, and, nor, yet, or so) without using a comma before the conjunction, it’s a run-on sentence. • We ran the tests but the findings were inconclusive. • We ran the tests, but the findings were inconclusive. To remember this, memorize the acronym: fanboys, and when you write a fanboy word, check if you need the comma. –For, And, Nor, But, Or, Yet, So 15 These are ALL the coordinating conjunctions in English.