# Propositional Logic: 10 Tutorials

Logical System
###### 12/15/20

Indicative sentences in a natural language, English, for instance, are either true or false. For example, 'There are 35 State Governors in the U.S.A.' is an indicative sentence (which happens to be false). Such sentences express statements or propositions. Not all pieces of language express propositions. For example, the question 'What day is it today?' is not either true or false (although reasonable answers to it will be either true or false); again, the greeting 'Have a nice day!' is not either true or false.

Statements or propositions or sentences can be atomic or compound. 'There are 35 State Governors in the U.S.A.' expresses an atomic proposition; whereas 'There are 35 State Governors in the U.S.A. and there is one President of the U.S.A. ' expresses a compound proposition composed of two atomic propositions (one false one and one true one).

Propositional logic considers reasoning involving atomic and compound propositions. We will see later, when considering predicate logic, that propositional logic is a relatively coarse instrument. It ignores details which can be important. However, ignoring detail allows the resultant theory to be simple, elegant, and easy to understand. And it is a good representation for many cases.

It is also a good place to start when learning logic.

### Exercises

Each of the tutorials has its own exercises, which can be done quickly and easily out of their own web pages. However, sometimes a User might want to save a half-finished proof to come back to it later, or might want to print a proof, or might want to do totally new exercises not supplied here on this site. From a computer software point of view, those tasks are not easy to provide out of plain web pages. But, there is a web application 'Deriver' that will run out of a web page and provide those abilities.  Should you wish to use that, see Exercises for Easy Deriver using the Deriver Web Application . Good advice is: start these tutorials without out it, but if you get to the point of wishing to save some work, then switch to the Deriver Web Application.