 In more detail, the strong bond between quarks is known as quark confinement and it is sometimes illustrated with the “bag model”. The idea is to think of a quark triplet as if it was inside a stretchy bag. If you then try to separate one of the quarks in the triplet, you’ll discover that the bag resists your efforts with an increasing force. The energy that would be required to isolate a quark from the triplet is far greater than the pair production energy of a quark-antiquark pair. So, what happens is that before the isolation could happen, the energy being directed to the process produces mesons—quark-antiquark pairs. Instead of pulling apart a quark from a quark triplet you end up with a quark-antiquark pair (and the original quark triplet remains intact). Hence, it appears that the quarks in a triplet are existentially dependent on each other. It is important to see that this dependence among the quarks may not be purely causal. If there were independently existing quarks that sometimes get bagged together, then their mutual dependence would indeed seem to be merely causal. But given that we have never observed independently existing quarks, it seems that the existence of one quark necessitates the existence of another one. This is already enough for existential  dependence.[6]