Let's give this a try:
If I missed something, or erred in this, let's see if we can fix it.
1. Things that exist with certainty can be observed, described, and usually measured in some way. Essentially, we can see, touch, hear, or otherwise detect them directly. There is a high certainty level for their existence. We encounter such things constantly in our lives and most are quite familiar to us.
2. Things we theorize to exist may be observed by second level influence on things known to exist. An example might be sub-atomic particles which only make themselves known through the generation of other particles, even though they cannot be directly observed. Gravity is another example, which is known only from its effects on physical bodies. We are quite certain that these things exist, but are ready to change our minds if some other thing better explains a phenomenon.
3. Things we hypothesize to exist may be described through mathematical proofs or third-level influences on other things. These things have the lowest level of certainty, and are subject to question as to their reality. For example poly-dimensional things should exist, based on mathematical proofs, but are not observable directly, or even at second hand. We are not certain of their description, however, nor do we understand them fully. The precise nature of time, for example is still uncertain, although we believe it exists with a high degree of confidence.
4. Things we imagine to exist cannot be observed at any level. We can imagine them, but cannot experience them directly or measure them. In order for us to believe they exist, we must have "faith" that they exist. They appear not to exist in the physical world, and no evidence for them is available. But we can imagine them. These are imaginary things, and actually do not exist, except in the mind's imagination. Different people may imagine different things, and may be influenced by cultural and other influences. It cannot, however, be said that such imaginary things have any real existence. They are imaginary things. Not everyone believes that such things exist at all, but some people do have "faith" that they do. Often, imaginary things are used to explain things we do not understand. If we become able to understand those things, we no longer need imaginary explanations for them. History and science have demonstrated this in many instances.
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