Logical mathematics holds that "a declarative sentence that can judge whether it is true or not is a proposition". What are the conditions? As long as one person can do it, anything can be done.

As long as the statement can be judged to be true or false, it is a proposition. Whether we know it or not, as long as we can judge it. For example, it will rain in May 2050 1. We don't know whether it will rain or not, but on that day, we will know, that is, we can judge whether it is true or not. This is explained in both logical mathematics and discrete mathematics.