What is it that makes some mobile apps feel so compelling? Why is the skeumorphic design of some of Apple's recent apps so awful? Why do desktop apps feel dated? I came to my own answer to these questions while listening to Dan Benjamin and John Gruber complain on The Talk Show about the regrettable new version of the official Twitter app for iPhone.

Ever since I can remember, applications have presented to me interfaces. Even the best of them put graphics on a screen that clearly mediated the relationship between the user and the processing of data managed according to a set of rules. (The worst of them were exercises in trying to figure out how to manipulate a crummy interface to do the processing that you wanted done. A number of versions of Microsoft Word, for example, required hunts through menus and dialogs to try to determine the magical series of clicks that would trigger the right formatting or appearance of text. You knew what you wanted and that it could be done but not how to tell Word to do it.) Great apps could try to make you forget, through inspired design and new metaphors, but in the end you knew an interface was there - that there was mediation between the processing you wanted the app to do and the actions required to trigger it.

Touch computing makes progress on this front, as it removes at least one layer of artifice. If the interface doesn't lag, then selection and clicking feel like direct manipulation of data, not as though they are actions requesting processing, followed by a graphical response. A drag of the mouse and a click of its button are abstract, obviously actions you intend the computer to observe and respond to. Touch rids us of this, but the way forward requires more.

I believe that the best apps will be designed as complete objects. They will have an internal physical consistency, a logic of manipulation, that will make using them feel – not just look – like using a *thing* rather than putting in a series of requests. When you pick up a new object in the world, you look at it, turn it over, fiddle with it. You try to figure out what it can do, how it interacts with other things, and you gather this from its shape and how it responds. Think about picking up a book, a Swiss Army knife, a jewelry box, or anything else you happen to have around you. All these are designed, to be sure, but you learn how to use them and know their limits by the physics that apply to everything else in the world. How they are put together dictates the rules of your interaction with them, and you just know those rules because physics are everywhere and the object is right there, exposed in front of you.

I keep coming back to this when I think about what makes the Twitter for iPad app so compelling, even though it has significant flaws. That app, with its sliding drawers, just hints at a semblance of being a complete thing unto itself. You feel, when the app is at its best, that you are playing with an object, that obeys known, physical rules. You are not requesting some data processing to be executed and to report back to you.

Now, Twitter for iPad is not perfect. Tapping a tweet to see a conversation feels like a request, not a physical revealing of a conversation from the germ of the tapped tweet. Doing a reverse pinch to expand a tweet into a profile, figuring out whether to hit the tweet itself or the picture of the Twitter user, and some of the sliding don't feel particularly intuitive or connected to an easy to understand set of rules. But the potential is obvious. With more attention to detail, using Twitter can be like using a real thing, like a magical set of cards but where that magic has simple and clear rules and bounds.

Although Twitter for iPad feels a little like sliding cards on a desk, it doesn't try to replicate that experience - and it certainly doesn't look like a desk covered by paper. Flipboard may even be a better example. It doesn't act like any real book, and yet turning "pages" is so addictive, because it just feels manipulative, not input-output driven. That probably gets at it best, that it's the feel of using these apps, not the look of the animations in itself, that makes them seem so right.

Indeed, the best apps will likely not take many graphical cues from the real world objects they logically resemble. Criticism of skeumorphic designs in Lion, like address book and calendar, and in iOS, like iBooks and Find My Friends, are rampant and on target. Although I think Steve Jobs was right relentlessly to focus on making the user feel like he or she was using a real object rather than a computer, these Apple apps make clear why mimicking the appearance of a real object is often a lousy way to do that. A book reading app will never be a book, and we shouldn't try to enlist the user in pretending otherwise. It's like putting wood panelling on a TV or making a car look more like a buggy. No thing will ever be great masquerading as something else. They can only disappoint when the physics and rules of the app diverge from the real thing. If it looks just like a calendar and I can't tear off pages, circle dates, flip back and forth, and the like, it will feel like I'm using a poor facsimile of a calendar. I'd rather use a new kind of object altogether.

The object oriented app will have a consistent, internal physics. It will have a simple and bounded set of interaction rules. And most importantly, using it will feel like manipulating a thing. We will use the app to make things happen directly, not as a remote control for sending messages in order to receive other messages.

I don't know what these new apps will be, but I do know that we've glimpsed their birth.