You know how sometimes when you're reading, you'll come upon a word or phrase you've seen all your life, and see it in a whole new light? All the sudden, you really see it, as if you had just learned it for the first time. I do this all the time. I'll see the word "rooster" and think, "Oh...they're called that because they roost." When I moved to Louisiana, where people often have real, hinged shutters for their windows in case of hurricanes, I realized shutters are named for what they do--they shut.
A while back, did this with the word "past", as in, "That's all in the past." The word is a noun here, but this time it looked more verb-y to me. I realized "past" sounds like "passed", and started wondering if that's actually where it came from. Turns out it does, at least according to this amazing amateur etymological dictionary. Before the late 1500's, people said an event from a previous time was "passed", and they eventually compressed it into "past". The newer word is generally used as a noun, so we don't recognize the sense of motion conveyed by "passed". Looking at the word's history reveals that it's based on a metaphor, which treats the passage of time as something physically moving by us. Time past is time passed.
In fact, this metaphor is so common, it's hard to see it as a metaphor at all. We say things like, "That's all behind us now" without ever realizing that we're speaking metaphorically. But we are--what's in the past isn't really behind us in a spatial sense, any more than people in higher tax brackets are physically above us. But time is a tough thing to think about, so it's a handy shortcut to think of it in terms of space or motion; as something that moves through space. Even when we think of the past as a noun, we're still thinking in spatial metaphors. We imagine the past as being like a place, even though though it really isn't in any simple sense (yes, Einstein showed that space and time are two sides of the same coin, but that's not exactly intuitive to most of us.)
So, we think of time as something moving by us or as a place. That's two spatial metaphors for time, and there are probably a bunch more. Why do our minds work this way? Why do they use spatial analogies to make sense of more subtle abstract concepts? It makes sense if we consider that way back when brains first evolved, they weren't used for abstract thinking. They were for helping animals move around in space. A fish's brain, for example, is mostly for coordinating its senses with its movements, so it can swim around, find food, and avoid predators. Brains were originally very much about the physical world. So, it's no surprise that when some animals started thinking abstractly, they used the framework already in place for navigating through space. In the case of humans, we started thinking of time as being analogous to space.
We think of other abstract things in spatial terms, too. Good is up, and bad is down, even though good things aren't necessarily above bad thing. "That guy is the lowest of the low," we say, even if he's 6'5". Status is also seen in terms of up and down. We say a colleague "rose" in the corporation, even if--spatially speaking--they merely moved sideways down the hall. We speak of people falling from grace, lifting themselves out of poverty, and being part of the upper crust. The metaphor is so natural, it's hard to even realize it is a metaphor. It's even hard to avoid using spatial terms. Try saying that someone has high status without using a spatial word like "high".
Of course, we think with other metaphors besides spatial ones. In addition to thinking of goodness in terms of "up" (her reputation was above reproach), we also think of goodness in terms of cleanliness (her reputation was spotless). Conversely, bad is not just down, it's also dirty. A swindle is a dirty trick as well as a lowdown thing to do. Anger is heat, or internal pressure: "She's boiling mad." A test can be "hard" even if the questions are printed on silk, and a rock-solid bodybuilder can be "soft" on his children. It goes on and on. Once you start noticing this sort of thing, you see it everywhere. Proofreading this post just now, I noticed that I had used the word "hard" for "difficult" twice in the previous paragraph. I was unconsciously using metaphors to talk about how we use unconsciously use metaphors!
Language is full of metaphors (even though language is not bucket-shaped, and can't literally be full of anything.) And it's not just the clever new metaphors that poets try to come up with, but old, fossilized ones that no longer strike our fancy. When I say I'm looking forward to getting a new computer, nobody says, "What an interesting way to put it!" Maybe they reacted that way the first time someone said it, but I doubt it. The "time = motion or path through space" metaphor is probably wired into our brains. But language is full of other metaphors that probably did seem clever at one point, and go unnoticed now. The first time someone said "She's very bright", instead of "She's very intelligent", it may have seemed like a catchy turn of phrase. After a while, the new metaphor (luminosity = intelligence) turned into a standard, alternate meaning of the word "bright".
This is one way the meaning of words evolves. Think about the words "past" and "passed" again. Pass came from the Latin word passus, meaning "step" (this is also where the word "pace" comes from). In Old French, it came to mean "walk", and in medieval English it came to mean "move by." That's what it still means in modern English, but it can also mean other, more abstract things. Today, if we say we passed an exam, we probably just mean we didn't fail it. We can say it without thinking in terms of moving past the exam to other things, but that's where the usage came from, and realizing it gives us a brief glimpse of the way our ancestors conceptualized the word.
Looking at language and thought this way is fascinating to me because it adds so much depth (another spatial metaphor). This viewpoint lets you look under the surface, to see the cogs and gears underlying our words and thoughts. Plus, there's always that pleasure of finding connections. I never though about "past", "pass", and "pace" as being related until just a few days ago, but the discovery was rewarding, and my view of how English speakers think and speak will always be just a little richer for it. Well...richer in a metaphorical sense, anyway.
A couple of good reads about this stuff: