One switch, two messages

A switch has two positions: down, or up. That is the whole switch.

A sender sets a switch. A reader looks at it. These are its two ends.

A bit can be pictured as one switch with two states. A state means something only if both ends agreed first.

A state is one position of the switch.

We write the two states as 0 and 1. The name is short for binary digit. A digit is one of 0 to 9. A binary digit is only 0 or 1. Nothing inside the switch looks like a digit.

One switch, read once, cannot tell three messages apart. The switch has only two states. "Now", "later" and "not at all" need more.

Can one switch say it?