Why must everything be an object in order to be defined?
For instance what exactly is a thought? Is it an object, concrete and tangible?
What is an emotion?
What is space but the absence of objects and yet we can define it.
To exist is to exist as SOMETHING. That is objective.
To comprehend that something exists you do what? You abstract a sense of it conceptually.
Your concept is a compression scheme to fit the universe inside your little head when it would not otherwise fit.
A rational mind checks often to see how well the concept matches the reality. It does this by means of the senses. That is what the word "ostensible" refers to.
What exactly is a thought?
A thought is brain activity which places objects before the mind to be understood for pro survival purposes. Survival consists of neotiating with reality. Knowing the difference between what really IS as opposed to what you wish that it was is sanity.
What is an emotion? It is an involuntary physical reaction to values you hold. The greater the value (be it positive or negative) the greater the physical reaction.
When you say you "fear" something it means you involuntarily react to the valuation of danger you've learned to connect with an object or situation.
What is space but the absence of objects and yet we can define it.
You shot yourself in the foot on that one. Without OBEJECTS (objectivity) all you have in your head is space!
Notice how unconnected your thinking is. Let us put your first sentence next to your last sentence.
Why must everything be an object to be defined? (You answer your own question with this: (What is space but the absence of objects and yet we can define it?)
I must say these are very very basic definitions.
It is by means of objects that fit what we are (real and objective) into the world of actuality (real and objective). Where people get confused is when they don't understand HOW THEY DO IT! This is basic epistemology: What do we know and how do we know it.
If you have not bothered to sort through your foundational definitions I don't wonder you are easily confused!
Life without a strong (accurate) sense of reality is just wishful-thinking.
Mixing fantasy up with reality confuses you.