This is world building stuff. It's important to keep in mind that this is way more nuanced, especially in real life. That nuance could also help with whatever you're making, so keep that in mind.
Hard Class Systems: Think aristocracy, caste systems, royalty. You're born into this, besides a few exceptions, there's really no way up (but a lot of ways down).
In these, your biology MATTERS what family are you from? Where are you from? And if you're illegitimate? Or even the child of a noble and a commoner? You're done, everything is over before it started.
"B-But my society has a hard class system and they understand that you can't control that stuff!!" (I have genuinely had someone say something similar to me, hence why I'm writing this actually, I have a point to prove)
Then why is it a hard class system? I could accept this in a Blend or Soft System (both below) but you can't have hard class systems without something that gives the upper class a way to set themselves apart from the rest of society. And it's almost always genetics that do this (I've actually never seen hard class systems done without genetics involved but I'd love examples if anyone has one).
Soft Class Systems: Basically what the American Dream was trying to sell us; if you work hard and put in enough dedication you have a shot at going higher in the ranks and being wealthy. In practice, these usually are much more of a scam.
If you wanted you could make this promise of earning what you deserve more concrete, but I don't think most people reading this want to form utopias.
Unlike Hard Systems, these can get more diverse, less genetically involved. You can have the occasional generational wealth but these are the guys that earn it. They usually don't leave behind a fortune for centuries and their monetary empires crumble after about 2 or 3 generations, 4 if we're stretching it.
The Blend: This is stories where a commoner can be really rich or have some type of societal power but they're still below nobles and such. These 'commoners in power' can work in many fields; maybe they're a military officer that rose in the ranks; a scientist who is well-trusted by the elites; or someone that has control over a powerful criminal syndicate.
It's set apart from Hard systems by the fact that the common people have more rights to opportunity. And it's away from soft systems because aristocracy still have something that this society believes sets them apart from everyone else.
