Can I paint over semi gloss paint with satin without priming it?

Yes you can. You need to be sure the surface is free of oil, wax, dirt and loose paint.Can I paint over semi gloss paint with satin without priming it?
Maybe! The thing you need to remember is this...if the semi gloss paint is an oil base paint you will need to use oil base paint in a satin too. BUT if the semi gloss is a latex base paint then you can use another latex type over it. PLUS, if you want to use latex over oil you MUST prime it first or the paint will peel right off. Hope this helps.Can I paint over semi gloss paint with satin without priming it?
Definitely yes. As with any enamel(paint with a sheen)you need to scuff with fine sandpaper, wipe down to get residue off. I make sure of good adhesion by sanding then using a liquid sandpaper (they are great). You do not really need to sand, just scuff the surface. You could use tsp if your walls are dirty or grimy- make sure it is non rinsable or you will have to rinse.
yes you can. You might want to take a fine sand paper and go over the walls. then wipe it down to make sure there is no paint dust. This will help the satin adhere better.
I wouldn't it will take a few coats and not neccessarily adhere well