I was having this debate with Rosti on IRC the other night, and I thought I'd continue the discussion on here seeing as some of you may find it interesting and have something to contribute. In summary, we were discussing which is the theoretically more logical behaviour for the S, Z and I pieces; 2-state rotation or 4-state rotation. Seeing as the ideal solution of having the tetrominos rotate about their true geometric centre is not possible -- as it would cause them to rotate out of alignment with the grid -- the two main alternative solutions are 2-state rotation (as seen in Pajitnov's original, the Spectrum Holobyte versions, the GB and NES versions, SEGA Tetris and its descendants, Atari Tetris, TetriNet, and others), and 4-state rotation (as seen in Tetris 2 + Bombliss, Super Tetris 2 and 3, Tetris DX, most other BPS versions of Tetris, and all guideline games after Tetris Worlds). For the time being, we're going to disregard wallkicks and high gravity, because they're an extra layer of complexity which may obfuscate the main line of argument. Rosti was arguing the case for 4-state, and insisted that having a constant centre of rotation, which lies as close to the geometric centre as possible, is the most logical and intuitive way to do things. As a result, the S, Z and I have 2 horizontal states and 2 vertical states. I argued that at low gravity, all S, Z and I placements can theoretically be made with a single vertical state and a single horizontal state, and it doesn't seem logical to have redundant states merely to provide a constant centre of rotation. I went on to suggest that a lot of players (myself included) don't intuitively think in terms of rotation about a fixed point anyway, and instead simply visualise going from one state to another. Rosti countered my claim of "redundant states" by saying that the two vertical states allow for faster finesse. But this seems like a non-argument to me; if you're going to introduce more states than the minimum necessary, just because it's faster, then why stop at two? From a theoretical viewpoint, introducing redundant states should be taken to the logical conclusion of Typomino. This is where we left off; Rosti went to bed and I went to brush my teeth. But what do you guys think? Is it logical that we must have two horizontal states because one is a 180 rotation of the other about a fixed centre? Or do people see them both as simply "a horizontal state" and regard one of them as being redundant?