A concept identifies a certain class of things; a proposition
asserts something about that class. Concepts give us
indispensable tools for thought and speech by grouping together
similar objects, actions, properties, and relationships. However,
a concept by itself is not a complete thought, and a word by
itself doesn't say anything.
Words need to be put together into sentences that express
propositions. One essential feature of a proposition is that it
is either true or false.
To assert a proposition, we need a complete declarative sentence,
with a subject and a predicate.
The following are propositions:
Jack is a Baptist.
Some birds fly south for the winter.
I would like a Jaguar XJ-S for Christmas.
The following are fragments:
The Pillsbury Dough Boy
Ran too fast for me to catch him
Was two blocks south of the library