Earth and water together
Water gives earth something to care about and earth gives water somewhere to put it. Scorpio's intensity finds Capricorn's structure useful rather than restrictive, which is not true of every sign, and Capricorn finds Scorpio's refusal to accept the surface account genuinely valuable in practical matters.
The shared quality is seriousness. Neither sign finds small talk restful, neither performs enthusiasm it does not have, and both regard most people as provisional until proven otherwise. Recognising that in someone else is a large part of the initial attraction here.
Cardinal and fixed
Capricorn initiates and Scorpio holds. Capricorn sets things in motion, usually towards a defined outcome, and Scorpio sustains attention on them long after Capricorn has moved on to the next objective.
The friction is that Scorpio does not release a subject and Capricorn does not revisit one. A grievance Scorpio is still carrying is, from Capricorn's side, a matter that was dealt with and closed. Neither reading is dishonest, and the gap between them is where most of the arguments live.
Saturn, Mars and Pluto
Capricorn answers to Saturn. Scorpio answers to Mars traditionally and Pluto in modern practice. That places the three most severe bodies in the scheme around one relationship, which is a fair description of how it feels from outside.
Saturn with Mars produces endurance and a hard edge in conflict. Saturn with Pluto produces a pairing capable of surviving a great deal and inclined to control rather than trust. The condition of those planets in the actual charts decides which is dominant.
Where it grinds
Control, from both directions and by different methods. Capricorn controls through structure, schedules and money. Scorpio controls through information, withholding and knowing more than it says. Neither party recognises its own version as control, and both recognise the other's immediately.
The second grind is expression. Capricorn is undemonstrative by habit and Scorpio withholds by policy, so a relationship can run for years in which both people are committed and neither has said much about it. That works until one of them stops assuming.
What the sun signs cannot cover
A sun sign describes a tendency across everyone born in the same portion of the year, which is a population and not a person. Two couples with these suns can bear no resemblance to each other.
Moon against Moon determines whether the privacy each requires is compatible. Venus determines whether either offers affection in a form the other recognises, which is the recurring weak point here. Mars determines how the deadlocks resolve. Those matter more than the suns.
Questions people ask about this
Why do Capricorn and Scorpio form slowly?
Neither trusts quickly or volunteers information. The pairing tends to be settled internally on both sides well before it is discussed.
Is control the main problem?
Usually. Capricorn controls through structure and Scorpio through information, and neither recognises its own method as control.
Does Scorpio answer to Mars or Pluto?
Mars in traditional practice, Pluto in modern. Both are worth reading here, since they describe different things about how the sign operates.
What should I check beyond the suns?
The two Moons, then Venus and Mars. Venus in particular, because expressed warmth is the thing this pairing most often lacks.