In trying to understand the meaning of the word 'exist', I'm asking if there is anything exists that doesn't cause effects. Or is there anything that causes effects that doesn't exist?
If not then it seems to me that existing is the same state as the state of causing effects. Existence is conventionally defined as the state of having objective reality. Perhaps having objective reality is synonymous with having an effect on something?
A common view is to see Exists as a logical verb, rather than a theoretical one. When we say something like “snow exists”, it’s logically equivalent to the statement “something is snow”.
Whether this statement is true or not is thus a statement about the things that there are in the world, and it being true only implies a commitment to one thing being snow.
Another common view is Occam’s Razor - that we shouldn’t propose that the world contains more than it needs to than we need to understand it. This keeps things both functional and also helps guide a model of the world towards simplicity and ease of learning and empowering.
This is clearly related to the concept of existing things - we want to talk about the stuff that there is in such a way that helps makes sense of the available evidence - but it also makes sense to pull the logical terminology of existing apart from this programme of effective model building using the logic! Less successful models which talk about the stuff that exist can still be logical, and their associated pictures of the things that exist can still be coherent, even if there is disagreement and dispute about what we think the stuff of the world is. In fact, the ability to model the ontologies (the stuff that “exists”) of others is a huge step towards mutual understanding!
https://latex.codecogs.com/svg.image?\exists%20x(P(x)) Edit: sorry, that URL breaks. I don't care what people say, this SE needs MathJax.
I think given our common understanding of the word "exists", what you said is possible.
Though the thing that has no causal effects would be completely unknowable. Think of an invisible, untouchable dragon floating in your room.
David Lewis talked about such a thing in his discussion of Rae Langton's scholarship on Kant (Ramseyan Humility). He calls them "Idlers", which are
those fundamental properties, if any, that are instantiated within the actual world, but play no active role in the workings of nature.
Take a soul after the person dies: It has no effect that we notice. It may have no effect that the souls of other dead people notice. We don’t know whether it exists or not, there is no evidence, but because of its nature no evidence isn’t evidence of non-existence.
I’ll rearrange your question: If something has no effect, does it exist? Since it has no effect, whether it exists or not makes no difference to anybody. Except it might exist in itself and be quite annoyed that we don’t acknowledge it’s existence (but we would never know).
Now take an alien spy drone created by some vastly superior technology. It has no effect. It just exists and spies on us. At some point it flies home, turns a switch so that it has an effect again by reporting everything it saw. Did it exist while it was spying?
Only events can cause effects. Existing is not an event.
An event occurs at one point in time. Existing occurs over a longer period.
In an event something changes from one state to another. Nothing changes during existence.
