If there is a storm, then the beach erodes.

If the beach erodes, then there is a storm

If the beach erodes, then there is no storm

If there is no storm, then there is a storm

sometimes true and sometimes false

true

false

A PROPOSITION - FALSE

NOT A PROPOSITION-FALSE

A PROPOSITION - TRUE

NOT A PROPOSITION - TRUE

true

false

If you are not smart or not lucky, then you are not rich.

If you are  smart or lucky, then you are rich.

If you are not smart and not lucky, then you are not rich.

If you are  smart and lucky, then you are rich.