
This sentence is incorrect it is a run on.
This sentence is also incorrect, it is also a run on.
Really? ‘Tis true. The first sentence is a run on because it is two complete sentences put together with no conjunction, no semi-colon, no period—nothing to indicate the end of a sentence.
The second sentence is a special (and annoyingly common) run on called a comma splice: two sentences “spliced” together with a comma.
Because here’s the thing: “run-on” doesn’t mean long; it means you’ve got two sentences you smashed together, even if they are two tiny sentences.