The short answer
Two who like to be in charge, and only one chair. By the element rule, Aries is fire and Capricorn is earth — and the rule rejects this pair. Keep that in mind and read on, because the rule answers far less than it seems to.
Both cardinal, and both with natural authority: Aries leads through initiative, Capricorn leads through competence. When they split territory — he handles this, she handles that — this pair is as productive as any.
What the element rule says, and what I measured
The table every magazine publishes is simple: fire matches fire and air, earth matches earth and water. It was not invented yesterday, and it has a geometric reason — signs of the same element sit 120 degrees apart, and allied elements sit 60 degrees apart. Those are the trine and the sextile, the two aspects that tradition calls harmonious. The compatibility table is the aspect table applied to a single planet.
It puts half the zodiac on each person's list, which already shows how little information that is. And it can be tested against the numbers. I drew a random sample of 600,000 pairs of birth dates between 1966 and 2025, using the same ephemeris that builds charts on this site, and asked: in the pairs the rule approves, do the other pieces follow along?
| Between any two charts | Pairs the rule approves | Pairs it fails |
|---|---|---|
| The Moons match up | 49.8% | 50.0% |
| There's a Sun–Moon contact | 46.4% | 46.4% |
| There's a Venus–Mars contact | 46.1% | 46.2% |
| Contacts between the two charts | 26.7 | 26.6 |
The columns are the same. Knowing that the rule approves or fails your pair tells you nothing about the other person's Moon, nothing about desire, and nothing about how many contacts the two charts have. And 50.0% is exactly what a coin toss would give you.
That does not make the table false. It makes it small: it describes a trait of temperament, read from a single point on the chart. Using it to decide who to date is reading a book by its title's first letter.
Aries and Capricorn in practice: where this pair gets stuck
The square here is about who decides. Aries wants it now, Capricorn wants it on schedule; Aries treats Capricorn's caution as a personal brake, Capricorn treats Aries's rush as a threat to what is already standing. And Capricorn does not argue: he simply does not do it.
This pair gets better with time and worse with rushing, and that sentence is not a comfort: Saturn, which rules Capricorn, is the planet that collects on what is real. Where it sits in Aries's chart shows how much that collecting is going to hurt.
Your Moon changes sign every two and a half days, and your Ascendant every two hours. It is the difference between "we're Aries and Capricorn" and knowing what the two of you actually are.
Generate my chart for freeThe one thing your sun sign decides about the other person
There is one exception to "the table tells you nothing", and it comes down to pure geometry. Venus never moves more than 47.2 degrees from the Sun — it is an inner planet, and from Earth's point of view it stays tied to the Sun's light. Given your sun sign, your Venus can only fall in five signs.
So the distance between two sun signs decides the odds that both Venuses land in the same sign. Measured across the same 600,000 pairs:
| Signs apart | Aspect | Both Venuses in the same sign |
|---|---|---|
| 0 (the same sign) | conjunction | 24.3% |
| 1 sign | semi-sextile | 19.2% |
| 2 signs | sextile | 12.9% |
| 3 signs | square | 5.5% |
| 4 signs | trine | 0.8% |
| 5 or 6 signs | quincunx and opposition | 0.0% |
Aries and Capricorn sit 90° apart — a square — and that puts this pair in the 5.5% bracket. The two of you may well have Venus in the same sign, and it is the one affinity your sun sign guarantees, at least a little.
Notice what the table does with the element rule: it cannot follows the rule. Pairs the rule fails come out on top of the list, and pairs it approves come out at the bottom. The Venus link is real, and it is geometric — and it is why the compatibility table sometimes seems to work. It works a little, and not for the reason it claims to.
What no sign table can reach
Four pieces that change everything, and that no sun-sign table can reach:
- Each person's Moon. It is the way you feel, need and settle down — the piece that most decides day-to-day life together. It changes sign every two and a half days.
- The Ascendant. It changes every two hours and depends on the city. Two Aries born on the same day can arrive at a party in opposite ways.
- The house each one falls into on the other's chart. The same Venus in your house 5 and your house 12 is passion in one case and a private matter in the other. This layer needs both people's birth time.
- What each one has already lived. Age, past relationships and the timing of the meeting weigh more than any aspect — and none of it is in anyone's chart.
This crossing is what's called synastry, and it needs both people's date, time and city of birth. Comparing sun signs is what's left when you don't have that.
And the limit stated out loud still holds: astrology decides nothing for anyone, doesn't tell you to stay or leave, and doesn't replace conversation or therapy. It gives you vocabulary. A couple who discover that one Moon needs routine and the other needs novelty have gained a better question than they had before.
Frequently asked questions about Aries and Capricorn
Do Aries and Capricorn work well together?
By the element rule, no: Aries is fire and Capricorn is earth. But that rule reads one point on the chart out of the ten that exist. I measured 600,000 pairs of birth dates: among the ones the rule approves, the Moons match 49.8% of the time; among the ones it fails, 50.0% of the time. The chance rate is 50%. Your two Sun signs do not tell you whether the relationship works.
What is the aspect between Aries and Capricorn?
90°, which tradition calls a square. That is where the rule of elements comes from — it is the aspect table applied to a single planet. Signs of the same element sit 120 degrees apart, allied elements sit at 60, and the rule rejects the rest.
Can an Aries's Venus be in Capricorn?
It can, and it is unlikely: it happens 5.5% of the time. That window is the only thing your sun signs actually decide about each other's charts.
So what decides whether two people are compatible?
The crossing of the two full charts, which is what's called synastry: one person's Moon with the other's Sun, one person's Venus with the other's Mars, and the house each one falls into on the other's chart. None of that comes off a sign chart — it needs both people's date, time and city of birth.
Do any two charts have few contacts between them?
Quite the opposite: the average is 26.6 contacts between two charts, with a 6-degree orb, and across 600,000 randomly drawn pairs none came out at zero. That's why "we have so many aspects!" means nothing on its own. What a reading does with the 26.6 is weigh them, not add them up.
Aries and Capricorn at a glance
Keywords authority, deadline, the one chair
The numbers on this page hold for any pair of people, because they come from the sky. What does not show up in them is your case. Two charts bring 26.6 contacts on average, and what a reading does with them is weigh — which are exact, which involve the Moon, which fall in a house that matters. Without both birth dates, times and cities, this page describes two signs, not two people.
