No offense to optimisticDuelist, but...

https://www.youtube.com/watch?v=R74aSD0zs18

I don't think his take on Cardinal, Fixed, and Mutable Aspects is totally right.

I've been studying the Western Zodiac for a personal writing project that's been going on since 2017 (though my interest in the Zodiac has gone on for longer than that) and I've looked up what all three of those words mean.

Cardinal Signs (Aries, Cancer, Libra, Capricorn) are the signs of action, the initiators of ideas, the revolutionaries that instigate a movement. Month-wise, they're the start of every season. Fixed Signs (Taurus, Leo, Scorpio, Aquarius) are the signs of foundation, the stubborn mules who refuse to change, the brave souls who stand their ground to keep order. Month-wise, they're the conduit between the start and finish of a season, the 'lifespan' I guess you could say? Mutable Signs (Gemini, Virgo, Sagittarius, Pisces) are the signs of change, the adaptors to any and all scenarios, the innovators who like to try new things and share them with others. Month-wise, they end their respective seasons and make way for the next.

Applying this to Aspects in Homestuck is kinda-sorta easy, at least from my POV, but I may not be right. I'm not right about a lot of things, I realize, but this is still my take on the subject matter:

Cardinal Aspects -
Time - marches on, as the saying goes; now, I know that it's got multiple dimensions - like space - but it moves forward in terms of flow and we've yet to figure out how to go backwards or sideways, if there even IS a way for humans to do so. But Time itself moves forward and carries everything with it, from people to ideas to ways of life.
Life - is never stagnate, it marches on too and always finds a way, as a couple famous dudes in the first Jurassic Park movie explained. Now, I know what you're saying: that Life evolves in a myriad of ways, so why the hell is it one direction? Well, Cardinal doesn't necessarily mean 'one direction', it means 'initiation' and guess what? You can't 'initiate' something new unless you rebel against what's already made precedent. Why do you think Life is opposite of Doom?
Breath - on the heels of the whole 'initiation' thing, Breath is all about freedom and progression, running hand in hand with Life in the flowery field of Free Will. At best, it leads to independence. At worst, hedonism. In the end, it's what we choose to do with ourselves in life and that's pretty straightforward....most of the time, anyway.
Mind - when people tell you to make up your Mind, they're asking you to make a choice. Now, sometimes a choice can be taken back or changed before the consequences have time to take effect, but often times, that's not the case. There are things you do that you may wish you could take back, but can't. You've made them, done them, and nothing can be the same again unless you make another choice to fix it. Both definitions of Cardinal are best displayed in Mind, I think.

Fixed Aspects -
Void - it's always there, a nebulous blot where all the unknown/secret stuff hides until Light fishes it out. And even then, it's STILL always there, hiding stuff we've yet to discover and some stuff that we put there to hide from others.
Doom - no matter what time period we're in, how the rules are written, how the math is equated, systems and limitations are always there to lay down the law.
Hope - everyone has their beliefs and dreams, which all have essentially followed the same theme over thousands of years, from religious aspirations to personal goals. They haven't really changed. Narrative-wise, both a good friend of mine and my big sister have both said that every idea has already been done/used/written, all that changes is how it's presented.
Rage - pretty much the same as Hope, but with the opposite emotions involved: people get pissed over the same thing, time and time again, in more ways than one, and that's something that hasn't really changed much either.

Mutable Aspects -
Space - never stays the same, despite how it's portrayed in Homestuck. Think about it: a piece of land is always there, yes, but what about the stuff ON the land? Or a room, it stays the same, but the stuff occupying it doesn't. Space isn't just a location, it's what's IN the location and how the space in said location is re/arranged. It's our position and movement from place to place, our ideas in constant flux, the vastness of possibility that we all lay out around us. Space LOOKS like it doesn't move, but really, it does. Just not by itself.
Light - let's face it: what we know is always changing. We learn new things every single day, the spotlight shining itself in different directions the second someone realizes they found something worth looking at. We're never in the dark for long, because the Light is in our eyes, in our minds, always looking for answers.
Blood - relationships are dicey, tricky, and overall worth it in the end, because everyone craves a connection of some kind and those connections change over time, depending on the choices that we make. A friend can become a lover, a lover can become a friend (in the best case scenario, anyway), or sometimes an enemy (in the worst case, which nobody wants or likes).
Heart - our personalities aren't always set in stone. We put on a different hat each day (I use hat instead of mask, because Hats are symbols of Heart while Masks tend to lean towards Rage. Don't believe me, look at the symbol for Rage, and I mean REALLY look at it), depending on how we feel. Sure, we're all ourselves and no one else, but how we feel when we get up in the morning can change once we've had breakfast or get a phone call or turn on the TV to view the news. Our emotions are constantly in flux, never Fixed or in a straight line. Trust me, I'm a very moody person who struggles with depression, I know this very well.

The Cardinals flow together, the Fixed have Hope to anchor them, and the Mutable fit in a cyclical flux.

To me, they fit better that way.