This is an old post but I wanted to give my experience with it in case anyone, like me, stumbled onto this via a search engine b/c they're trying to get to the bottom of their Merc squ Asc as I am now. Discovering this has realllly shed light on most of my social and communication issues.
I can't remember how many comments above I wanted to second. Which is strange b/c my Mercury in Cap gives me a mind like a vice. I can remember what time to the minute innocuous things happen around me (for example last night, my parents were wondering aloud if they fed the dog or not and I said "you did, it was 4:25").
I don't know when I'm exaggerating my intellect vs. when I'm selling it short, but I really feel like I'm clearly brilliant but for some reason that's not clear to people around me. And yes, I do feel like 'everyone's an idiot' as almost every article on this aspect explains.
Because of the MC, I can even have a real silver tongue when I need to. I once talked down five security gaurds with tazers (wanting to use them) and made 4 of the 5 shake my hand afterward. I'm good with cops. I'm the nicest possible person at work, however stilted and obviously disingenuine (cause I'm still locked into my condemning view of others). I read that Merc in Cap's can "see grass grow", which I took as saying "sharp."
But being misunderstood has realllllly warped a lot of the good of that, especially socially, in my life. I can remember even as a kid (before I knew about any of this) yelling at a family member "YOU'RE NOT LISTENING TO ME!!!" I have that message playing in my head all the time.
I may be extreme on that end b/c my S. Node is almost (just outside of 10 degrees) conjunct my MC. So on top of all that, it's like even the good that I maintain my Mercury has?? Out the window, destiny-wise. Ouch.
Strange that I found this on a search engine when I'm a posting member here. Maybe it's a synchronicity-lesson for me and posting this will transmute some of the malefics about this. B/c you can peruse my posts here (I haven't made many) and see just how much an "unlistened to" Mercury MC Cap square Asc goes way too far in their communication, saying way too much at times, hitting five million different topics that drag the whole message down like a jenga tower at the end of the game.
~*sssssSSSssssss*~
It's hard to know, with this square, what to say and when to say it. If it goes down this path without being taken care of, as I feel it has, it becomes painful to communicate; thoughts are like liabilities when not kept in. My attitude towards it is, at this point, the same as towards bodily functions. The lone bright side I'm feeling about it as I write this is that... well it is cool to have been (forcibly) taught by this aspect that communicating must be done for basic health reasons. That is a pretty wild and meta-physical truth I may not have know. It can become like 'communication constipation' to cope by refusing to communicate. I'm very sorry but I am speaking as you read this in the same way I'd use the bathroom or belch. I'm hoping that this word practice in self-awareness will transmute it into a tough lesson, instead of just tough sh!t. And then I'd be able to use my communication to be of better service to others, rather than fulfill one's own backlogged unmet needs.
The original post mentioned relationship issues; I am pretty sure this is a huge reason every single gf of mine has walked away feeling sort of 'wary' of my mind. By itself, this aspect is not very good for harmonious intercommunication. It's almost unpalpable as much as unmistakeable: every word I express, every willful expression I make, is designed for Ascendant identity reasons. Disingenuity is probably hard for a listener to prove, but easy to feel.
I in fact doubt my own mind and communication way more than my emotional side; the latter is what I rely on far more to get through actual life challenges, while the former I keep tightly to myself until it needs to be employed.
This is something I've experimented with throughout my life, relentlessly at times ("I'll be stoic" no "I'll only say something funny" no "I'll only speak in such and such a way" no... disingenuinity city!!). Then I'll binge on a refusal to communicate. Art and music have saved my *** in that way (though with the S. Node MC, even those things have been forced into a mere 'good for me' and no one else status).
The way I'm feeling about this now, getting to the bottom of it (hopefully) is that.... this aspect, as somewhat innocuous as it seems, can really break your identity in some deepseated ways.
PS: At the "sssSSSSsss" page break above, I stopped typing and went for a walk with a loved one. During the walk, the loved one asked me a question. When I answered it, they went on "no, no, I'm not sure if that's it..." kind of meandering, doubting my words. That's fine. I wasn't sure if I heard their question right. This went on, back and forth, for several minutes, them meandering in a totally inept way, and we both came to realize/admit that yes, what I originally said was the right answer, and they were confused. I realized that that moment was a clear case study in the issues I was just typing about, and that it was a full on synchronicity from the 'Tao' to help me see this issue played out more fully. When I realized all this, I made a point to say "this happens all the time; what I first said was right, if you'd have just listened." Not sure htat was the right way to handle it, b/c I felt very low and distant and wanted to be alone for some time after it, then had to exert effort to get back to a warm persona rather than my disappointment at being doubted souring the whole time. B/c that's the potential of this malefic, to just withdraw completely when it hits you on the nose. So I sincerely considered this a moment to learn how to handle this better.
I couldn't not say this, b/c of the timing. This is a case study in how a pattern like that can turn into a trigger for withdrawal (not wanting to "ascend", or let your personality out into the world, where foolishness always has the microphone).