When you refer to an ideology with a capital letter does that make the reference related to a prescribed ideology? And when you make a reference in the lower case does it make it just a personal disposition? And why do none of my rock cakes turn out right?

Luncheon meat goes down very well with cherryade.

Do you mean as in, "The British army marks time, whilst the Red Army Marx time?" (well - it used to.)

As to your second question, try putting some tooty-fruity in them.

Perhaps because those with capitals start - as with Marxism - with someone's name, but existentialism is just personal. If Sir Real had been a painter, the movement would have taken Das Kapital.

If you will insist on mixing those two comestibles what hope could there ever be for your rock cakes?

Communism, as a generic theory, would be lowercase, as the ideology of a ruling elite or by others who support that specific ideology it would be capitalized. Thus you might say that early Christians practiced a form of communism, holding property in common and supporting each other financially. The Supreme Soviet of the USSR practiced Communism.

More about the generic and the specific.
Existentialism has no single figurehead unless you take the anti-hero from "The Outsider" whereas Marxism has a man with a big beard and shifty eyes. Does the capital letter signify a form of ownership?

Tooti-fruitti? I'll give it a try and get back to you....

Luncheon meat goes down very well with cherryade.