Strong vs. Valid argument

 Whether an argument is valid or strong does not depend on:

• Whether the premises are true.
• Whether we know the premises are true.
• Whether the person making the argument thinks the argument is valid or strong

For example, this is a valid argument:
-Suzy is allergic to peanuts. So she will not eat a peanut butter jelly sandwich. 


This argument is valid but not strong. The premises might be true, but the conclusion may be false. Possibly Suzy will eat the sandwich without the peanut butter or she can have almond butter instead. Or maybe she is taking medication to help her fight her allergies and therefore she can eat peanuts.


Now here is the same argument, but told in a different way:
-Suzy cannot eat peanuts because of her allergies. So she cannot eat a peanut butter jelly sandwich.


This argument is strong because the premise is believable and so is the conclusion. Because of her allergies, Suzy cannot eat the sandwich.