Progressing with the progressive

Too many people these days acquire their knowledge from the internet but the quality of such knowledge is dubious. It's true that you can learn a lot from the internet - I am the grateful recipient of life-saving knowledge from the web. Recently, I climbed up the roof of my house with the wrong ladder and I couldn't climb down. After that experience, I went on YouTube to arm myself with information on ladder safety and the many different kinds of ladders and I have just ordered (through the internet again) my new ladder which will be delivered tomorrow. That is the kind of knowledge you can gain from the internet. 

I don't normally read Quora but yesterday, I received an email from Quora on a subject that was of interest to me. So I clicked on it and I was brought to a whole new world that I never thought existed. It was a world of the blind leading the blind. Someone asked in Quora the question 'Why is it correct to say "I am having a party tomorrow" but incorrect to say "I am having class tomorrow"?'