Tumblers full or empty ?

In order to clarify this, we look at

Example 1: Five tumblers

The following five tumblers will be divided into two classes: full and empty.

It is obvious: tumbler 1 belongs to the class full and tumbler 5 belongs to the class empty.

To which distinguishable unique class do the tumblers 2, 3 and 4 belong? These three tumblers are neither 100% full nor 100% empty. When we take a crisp decision then they belong neither to full nor to empty.
Indeed, the following can be noticed:

• Tumbler 2 is 75% full, thus it belongs with a grade of 75% to the class full.
• Tumbler 3 is 50% full, thus it belongs with a grade of 50% to the class full.
• Tumbler 4 is 25% full, thus it belongs with a grade of 25% to the class full.

Or with other words:

• Tumbler 2 is 25% empty, thus it belongs with a grade of 25% to the class empty.
• Tumbler 3 is 50% empty, thus it belongs with a grade of 50% to the class empty.
• Tumbler 4 is 75% empty, thus it belongs with a grade of 75% to the class empty.

In the following, we will find a class that covers all tumblers on the globe.