Sense Perceptions or Definitions

So when thinking about my question from ITT we locate truth I started to get caught up in concepts of truth, empiricism and rationalism, various takes on arguments and meaning, and a wealth of other bullshit topics. I would like to be able to filter off the bullshit, however, and simplify the conversation to be easily understood and approachable.

So I think I have, perhaps, the simplest way of asking my truth question. Here we go:

The sole proof for the existence of X is a definition.
The sole proof for the existence of Y is a sensory perception.

Is the existence of X or Y more likely? Why?


Here is where this came from:
I like Spinoza. The problem people have with Spinoza is that in The Ethics Spinoza argues from first principles, definitions and axioms, to get propositions. So when Spinoza writes "God, or substance, consisting of infinite attributes, of which each expresses eternal and infinite essentiality, necessarily exists." people will commonly reply "Great. But that does not mean that god exists." despite the fact that Spinoza has provided a coherent, consistent series of definitions and axioms which support his claim.

In a seemingly unrelated conversation people who like the coherence theory of truth will state that truth is found in coherence of ideas and states of reality. So, the statement "the cat is on the mat" is true if the cat is on the mat. How do we know if the cat is on the mat? We fucking look.

But wait. Spinoza's argument for the existence of god is supported by definitions and axioms. A common person's argument for the existence of a cat is supported by sensory perceptions. Where Spinoza has his definitions a common person has visual sensory perception, tactile sensory perception, olfactory sensory perception, gustatory sensory perception, and auditory sensory perception.

So where one may raise the criticism "Definitions do not prove that God exists" I think it sensible to raise the criticism "Sensory Perceptions do not prove that cat exists."

What makes a definition weaker than a sensory perception? At this point the only answer to this question I can think of is "preference". But if the entire enterprise of human experience is supported by "facts" and "truths" which are, themselves, supported by little more than preference...well, fuck.