It's important to understand that definitions are not assumptions. Definitions and assumptions are two different things. Now, we could also define them to be the same thing if we wanted, but typically definitions aren't about truth. They're about meaning.

Now, if you'd rather use "logical tautology" that's fine by mean. It's close to what I meant. "Evidence" and "Truth" are very semantically related... so much that your statement earlier is almost a definition, not an assumption. By definition, Evidence is something that indicates truth. Again I think the word reliable does make the statement an assumption. But again, I don't see where science ever made the assumption that evidence is reliable...

As for your second example, it is not much better. I will again attempt to show you the problem with your argument.

>solid objects are in fact not solid, they are mostly empty space. So the assumption that "solid appearance indicates solid" is actually false

For your argument to hold, your definition of solid in your second statement must be incongruent. I'll try to show how.

> solid objects are in fact not solid, they are mostly empty space

Here you've tacked on some definition to the word solid. That added definition being: "they are mostly empty space". Now let's look at your next statement

>So the assumption that "solid appearance indicates solid" is actually false

This only logically true if you use two different definitions of the word solid. Otherwise your statement is nonsense, when substituting your implied definition of solid:

something that appears as not empty, but is in actually mostly empty space appearance indicates something that appears as not empty, but is in actually mostly empty space is actually false