the difference being a gerund has the quality of "a continuous state of being"
joe wasn't fishing yesterday, and might not being fishing tomorrow, so fishing, wasn't for joe, a continual state of being.
But Helen if "he is running" isn't running a gerund? It doesn't say anything about whether he was running yesterday, will run tomorrow or what is chasing him.
It's confusing.
umm is THAT a gerund? cos grammer continually confuses me