By dkl9, written 2025-141, revised 2025-141 (0 revisions)
It's equally easy to walk left as right. It's much harder to walk up than down.
Both left/right and up/down are pairs of opposites. But the former is symmetric, and could be just as well reversed. The latter goes across a clearer, deeper difference, and only makes sense one way. Any other dichotomy is, in that way, like left/right and up/down, and so may be called "lateral" or "vertical", respectively, by metaphor. This is only a partial definition. Other defining aspects of the split will be clearer later.
These pairs are also lateral:
And these are also vertical:
Pairs with both sides equally common tend to be lateral, while pairs with one side much more common than the other tend to be vertical. Thus is enter/leave lateral, for you enter a place as many times as you leave, except at birth, death, and destruction. Thus is female/male lateral, for each makes up about half the population. Truth/lies is vertical, for there are far more false statements than true, at equal length, as is clean/dirty, for any use could make something dirty, but only intentional cleaning takes it back.
Pick some well-defined X, contrast it with not-X, and the dichotomy would generally be vertical, such as permanent/temporary and human/animal. Good/bad and fast/slow come from X/not-X patterns, but they're still lateral pairs, sith the medium point in each — morally neutral, or normal speed — is somewhat arbitrary.
When you can put numbers on a dichotomy, a difference in sign tends to be lateral, while the difference between near-zero and significant positive tends to be vertical. Walking left and walking right take the same power, applied in different directions. Walking up takes force from the body to oppose gravity, but walking down is passive — you just fall. Likewise can we grasp positive/negative charge and push/pull as lateral. Likewise is refrain from/select vertical, where the number is the information that the choice adds, and cold/hot, where the number is the amount of molecular movement.
Zoom in enough on some vertical pairs, and you make them lateral. Cold at its extreme means stationary molecules, but in daily life, cold/hot reduces to cooler/warmer across some dozens of kelvins, which is a matter of mere direction. Zoom out enough on some lateral pairs, and you make them vertical. Fast and slow are two directions from a medium point, but the extreme of slow is infinite time, i.e. permanent.
Sith lateral pairs are easily reversed, it's harder to learn relations between them. Hence the mnemonics for cation/anion ("t" looks like "+", "n" for "negative") and vector directions (right-hand rule), which both come from lateral pairs. Longitudinal/transverse are just two directions, and primary/secondary have equal scope, so it's hard to remember which type of wave has which synonym.