One criteria of concrete entities is that they bring about effects. The antithesis of this, abstract entities (all non-concrete entities), therefore does not bring about effects.

But, many commit to abstract entities, which they claim have effects, and therefore ontologically exist.

For Aristotle, these are secondary substances. And for Meinong, these are subsistence. And Quine highlighted these ontological commitments to show how they are needed to keep such philosopher’s frameworks coherent.

My English teacher at high school taught me that there are more exceptions to the rules than rules themselves. I think Western philosophy is like this as well. This is perhaps English and philosophy’s strength, but more likely their weakness.