Formal Declarative Proposition

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A Formal Declarative Proposition is a logic proposition that is mapped to a truth value.




    • Logical statement is a declarative sentence that is either true or false. A statement differs from a sentence in that a sentence is only one formulation of a statement. There may be many sentences expressing the same statement.


  • (Wikipedia, 2010) ⇒
    • In logic a statement is either (a) a meaningful declarative sentence that is either true or false, or (b) that which a true or false declarative sentence asserts. In the latter case, a statement is distinct from a sentence in that a sentence is only one formulation of a statement, whereas there may be many other formulations expressing the same statement.

      Philosopher of language, Peter Strawson advocated the use of the term "statement" in sense (b) in preference to proposition. Strawson used the term "Statement" to make the point that two declarative sentences can make the same statement if they say the same thing in different ways. Thus in the usage advocated by Strawson, "All men are mortal." and "Every man is mortal." are two different sentences that make the same statement.

      In either case a statement is viewed as a truth bearer.

      Examples of sentences that are (or make) statements:

      • "Socrates is a man."
      • "A triangle has three sides."
      • "Madrid is the capital of Spain."


Every “If p, then q” statement has an equivalent statement; this second statement is known as the contrapositive, which is always true. The contrapositive of “If p, then q” is “If not q, then not p.” In symbols, the contrapositive of is (here, the symbol ~ means “not”). To formulate the contrapositive of any logic statement, you must change the original statement in two ways.

      • 1. Switch the order of the two parts of the statement. For example, “If p, then q” becomes “If q, then p.”
      • 2. Negate each part of the statement. “If q, then p” becomes “If not q, then not p.”