There must be some word that describes that statement but i can't for the life of me work out what it is and its really bugging me.
All squares are rectangles but not all rectangles are squares.
All iPhones are touch phones but not all touch phones are iPhones.
I could go on, but im really keen to know what it is.
Added (1). River, I think you mean causal nexus, not casual. But i mean everyone makes spelling mistakes. Its better than the other answers, but im not sure that causal nexus is actually the term that you would use to describe this phenomena.