A proposition is a thing that can be true or false. In contrast, a non-proposition cannot be answered with true or false. Premises and conclusions are propositions.
Example of a proposition:
- Snow is white
- Snow is green
- I am hungry.
Example of a non-proposition:
- Ouch!
- Hello.
- Open the door!
- Is the door open?
Proposition Letters
In propositional logic, a proposition by convention is represented by a capital letter, typically boldface. For example, the proposition above might be represented by the letter A. 1
A: All elephants are green.
Proposition Vs Sentences
To determine a proposition, we typically need not just a sentence type but also a context in which the sentence is uttered. 2 For example, for the sentence type “I am hungry” to determine a proposition, it need to be uttered by someone. If Bob says it, it means “Bob is Hungry.” And if Carol says it, it means “Carol is Hungry.” Those are two different propositions because one can be true while the other is false.
Footnotes
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Smith, Nicholas J.J.. Logic : The Laws of Truth, Princeton University Press, 2012. Chapter 1.2 ↩