The dynamic
Square to each other, three signs apart, Aries and Capricorn are both cardinal, so both want to initiate, decide and run things. Aries is outgoing fire ruled by Mars; Capricorn is receptive earth ruled by Saturn. Aries wants to win now; Capricorn wants to win in ten years and still be standing. A technical link softens the square: Mars is exalted in Capricorn, meaning Mars energy works especially well when channelled through Capricorn's discipline. Capricorn shows Aries what its drive can become with patience.
The friction is about direction and pace. Two leaders means arguments about who sets the strategy, and Saturn's caution grates on Mars' urgency. Aries sees Capricorn as rigid, joyless or obsessed with hierarchy; Capricorn sees Aries as reckless and immature. Yet both respect competence and results, and they share a dislike of excuses. When they agree on a goal, Capricorn draws the long map and Aries supplies the burst of energy for each stage.
In love
Partnership tends to be serious and goal oriented: a shared renovation, career plans discussed over breakfast, a savings goal pinned to the fridge. Capricorn shows love through reliability and long-term provision; Aries through passion and protectiveness. Aries can feel Capricorn is too reserved, too busy, too controlled, while Capricorn can feel Aries is impulsive with shared resources. Comparing Moon signs helps, since Capricorn's warmth often lives there rather than on the surface. Humour about their competitive streak keeps the relationship from feeling like a merger.
As friends
Ambition is the usual glue between these two: training for a race, starting a side project, pushing each other's careers. Capricorn gives frank, useful advice; Aries gives a jolt of confidence when Capricorn doubts itself. Friction comes from Aries' lateness and Capricorn's silent judgment of it. A friendship built around a shared challenge tends to outlast one built on casual hangouts.
At work
Few pairings are more effective at work, provided the hierarchy is clear. Capricorn naturally manages, budgets and plans long timelines; Aries naturally leads charges, opens new fronts and handles crises. Clashes come when both want the final call, or when Aries skips the approval process Capricorn built. A written chain of authority sounds dull, but it lets both of them get on with the job.