"It is raining."
"'It is raining' is true."
Does "is true" make any difference? Thanks.
This link gives context to this question and testify that I'm not a nut (yet).
closed as off-topic by Edwin Ashworth, MrHen, aedia λ, Kristina Lopez, tchrist Jan 24 '14 at 23:39
The two sentences have a very different meaning, especially in light of the context you gave.
Betrand Russel was a high profile mathematician who, alongside a few of his contemporary peers (Whitehead, Turing, Gödel and a couple of others), were actively investigating one of the list of open mathematical questions that David Hilbert gave at the opening of the 20th century. Namely, whether there existed a set of axioms that we could build arithmetics on, in such a way that any proposition could be either true or false without permitting any internal contradictions.
Getting back to your statement:
Note the subtlety here, in light of the above-mentioned context: the first has a meaning in the sense that it has semantical implications. Namely on the state of the weather. The second also has meaning, but this time in the context of a logical grammar.
Here's a more convoluted example to illustrate how it is problematic when you assume that these two types of meaning (or implication) are congruent:
See where we're heading in the above?
The answer to Hilbert's question and how the above should be dealt with came in the form of Kurt Gödel's incompleteness theorem in the early 1930s: arithmetics cannot prove itself internally consistent. (Ergo, you cannot prove that there is one Truth, and ergo you shouldn't confuse logical truth with semantic truth.)
As @EdwinAshworth stated, this is most likely the beginning of a deductive logical argument which takes the form
The most common example is:
All men are mortal.
To reach a logical conclusion, each statement (or premise) must be true. So one must accept as true the premise that Socrates is a man.
Socrates is a man. is logically different that 'Socrates is a man' is true.