The statements or claims used in an argument
(the premises and conclusion) are called propositions.  

• propositions can be true or false
• propositions are expressed by declarative sentences

A sentence is declarative if it makes a statement, that is, if it asserts something.

• Amsterdam is in The Netherlands. 
• Textbooks are free in all of my courses.
• I have been in the Skinner Building before.  
• My computer was stolen.  
• The dog ate the steak yesterday. 

• There is a cat in the teapot.
• Hay un gato en la tetera.
• Er is een kat in de theepot

Many sentences can express the same proposition.

• I have taken logic before.
• I took logic.
• This is not the first time I have taken logic.

A single sentence can express many propositions.

• We saw the man with the telescope.

• No student solved exactly two problems.