In predicate logic, you are able to use either a single capital letter (R) for a sentence like "It is raining" or a letter followed by a small letter (Ra) which represents an atomic sentence.
In an atomic sentence in logic, there's one subject and a verb which is similar to the definition of a simple sentence in English language which also has a subject and a verb.
So, what does a simple sentence mean in logic if the atomic sentence is already the one with a subject and a verb?
Here's a quote from the text I was reading:
Simple Sentences: upper case letters
English: “It is raining”
Predicate Logic: “R”
Atomic Sentences: an n-place predicate letter followed by n lower case letters.
English: “Mary is tall”
Predicate Logic: “Tm”
What are some other examples of sentences represented by a single capital letter besides "It is raining" denoted by 'R'? If I am guessing correctly they should begin with a pronoun similar to "It" and "they" etc.