I have no ideas. I grasp a good many ideas. I’m acquainted with even more. Some ideas I understand pretty well. But none of them belong to me. Not even any I might have been lucky enough to entertain before anyone else. Even people who have discovered an idea or two didn’t create them. Sometimes the same idea first occurs to multiple people. Which could claim ownership? Both? All?
That no person can have an idea should be clear given that any idea you can think of has probably been thought of by others. My own study of philosophy includes many frustrating experiences of thinking I’ve found an original idea only to find that others are way ahead of me. Over time this experience has grown to be more amusing than frustrating. Others being acquainted with an idea presents no obstacle to many more discovering the same idea independently. The mere fact that different people can understand the same idea is sufficient to show that the idea itself can’t just belong to one or the other of them.
Ideas are their own thing. Ideas are entities just like sofas or skateboards. Except that they are abstract, their existence doesn’t depend on occupying space or time. And for just this reason, their existence doesn’t depend on someone creating them. As such, ideas constitute a commonwealth shared by all beings with the sorts of minds capable of grasping ideas.
Of course, we can grant up front that ideas are experienced differently by different people. This much is to be expected given that different people are different experiencers. We greet an idea with our whole mind, shaped as it is by our own experiences, habits of thought, predispositions. I grapple with the same ideas as everyone else when I learn to solve an equation for a value. For some the experience is pleasant, for others not so much. For at least a few, the experience will remind them or Earl Grey tea. There is so much variety among people and their experiences. Yet the ideas remain constant. The varying associations we may have with an idea are just facts about us in all of our differences, not indicators of variations in the idea itself. The idea is its own thing.
The fundamental ontological status of ideas is a long-standing matter of contention among philosophers. But regardless of basic metaphysical truths, when we think of ideas as being their own thing, a kind of entity, a whole new realm of inquiry opens up. Now we can examine an idea, analyze it, consider its implications, formulate arguments for or against claims about the idea. All we need to do is acknowledge that there is something to look into. Serious treatments of the ultimate nature of ideas all grant us this much.