So, what is direction, really? We can call it angular position, and we can call the change in angular position angular velocity, and we can call the change in angular velocity angular acceleration.

In case it isn’t obvious, there is a stunning symmetry with length here.  We can call it linear distance, where we can call the change in linear distance speed, and the change in speed acceleration.

Even more stunning is the fact that when we add direction to length we get position, when we add direction to distance we get displacement, and when we add direction to speed we get velocity.

Still, even in light of all these facts, there seems to be a winning argument (for reasons no one can explain other than the old “we’ve always done it that way”) that direction isn’t really a base quantity, like time or length. It’s supposed to be a thing that isn’t really a thing, whereas the other two are things that really are things. This approach is rather arbitrary, especially since direction can now be quantified as a scalar value or an amount, exactly like time and length are both quantified.