Two of the most frequent criticisms of social media hinge on the quality and quantity of information people disclosure through blogs, Twitter, Facebook and other social tools:

1. Why does s/he think anyone cares? Asked about people who blog their latest meal, tweet their random observations, check in on FourSquare, or share other pieces of information that would certainly fail to meet the New York Times standard of newsworthiness.
2. Why would s/he share that? Asked about people who blog about their mental health challenges, tweet about their sex lives, Facebook pictures of themselves half-naked, or share other pieces of information online that many people would choose to keep secret or private offline.

Underlying both of these questions is a seldom examined but widely held understanding about the relationship between disclosure and trust.

In offline culture, disclosure is both a creator and a signifier of trust. If I tell you about a difficult childhood experience, a sexual predilection, or a professional insecurity, my decision to share that secret with you implies (usually accurately) that I trust you. It’s a statement of faith in you personally: I’m showing that I regard you as a person who is capable of discretion, and as someone with something to offer that makes the risk of disclosure worthwhile — for example, sage advice about a work dilemma, or kindness and empathy for a personal trauma. It’s also a statement of faith in our relationship: I believe our friendship (or collegial relationship) is strong enough, and valued enough by you, that in constitutes at least as semi-private space in which information or emotion can be shared with an expectation that it will not travel further.

If disclosure is thus an expression of trust, it is also a creator of trust. When I trust you with a secret or a confidence, you may be more likely to trust me — if only because we are now in a situation of shared vulnerability. When I tell you something I wouldn’t tell someone else, I put you in an inner circle and create a sense of intimacy that allow further trust and intimacy to develop. It is the very fact that others are excluded — that my act of disclosure is particular to you — that makes the disclosure meaningful, expressive of trust, and trust-building.

Offline, anyhow. Online, it becomes much more murky. If I place you in a Facebook lists that gives you privileged access to stories or images I share with only a dozen other people, you may not know it — in fact, you’re likely to think that I shared that picture of my kid or that complaint about my period with the entire world. Even Google+, which distinguishes itself by making it easy to share different kinds of content with different “circles”, doesn’t make it obvious which circle a given update has been shared with, let alone how big that circle might be. If I’ve read a post because my friend has shared it with her “Extended Circles”, I don’t know which circles that includes, or who was in them (and interestingly, most people I follow on Google+ seem to post most things publicly).

The opacity of online disclosure, in which it is frequently hard or impossible to see how widely a given piece of content is shared, seems to lead us to the assumption that anything we see online has been shared publicly, unless we specifically know otherwise.  As a result, the disclosures we see online have very limited capacity to reflect or create trust: if you’re showing this picture to everyone in the world, or sharing this comment with everyone in our school or office, your disclosure in no way expresses faith in me or in our relationship. At best, it expresses faith in your network’s privacy settings, or its capacity to offer you a permanent “delete” option.

There are a handful of networks and tools that do create a greater sense of selectiveness among and between users. Path is based around the idea of limiting your network to 50 people — what an expression of trust, to know that someone has put you in that 50. Private Twitter accounts, in which you have to be personally approved before someone lets you read their updates, again impose a clear trust test: do I trust you enough to let you read my updates? But in most networks, it’s easier to communicate a lack of trust than an extension of trust: if I fail to accept your Facebook friend request, TripIt connection request or LinkedIn connection request, you may infer it’s a lack of trust.

How can we share in a way that communicates a sense of trust? Well, one tech option comes from  Google+ points an interesting way forward: if you share a post with only one circle, people in that circle see it as “limited”, and can tell who else made the cut to see this particularly detail. Ooh! Aah! you can think, as you read the details of your BFF’s latest date. Aren’t I lucky she shared that with me?

Or maybe not. After all, even a post shared with a limited circle of contacts is still shared with that all-seeing, all-knowing Eyes of Google. (Even more crucially, with the all-archiving database of Google.) How much could it mean for your friend to share a secret with you if she’s prepared to trust it to the Internets?

No wonder that we’re so deeply suspicious of online disclosure, then. All that rampant posting deprives us of a valued mechanisms for creating and expressing trust. In a world where people apparently share secrets freely, secrets lose their value as social glue.