Elementary is a deduction game for 3-6 players using an Aquarius deck. Each player will need some scratch paper and a pencil for taking notes.
Elementary uses only 20 cards from an Aquarius deck: one of each combination of 1, 2, or 4 elements. In other words, pull out 5 different single-panel cards, 10 different two-panel cards, and 5 different four-panel cards, and put aside the rest. (The easiest way to pull out the two-panel cards is to just find all the ones that are split the same way, horizontally or vertically.) Shuffle these 20 cards together, remove one without looking at it and put it face-down in the center of the table, and then deal the rest to the players. (Note that some players will be short one card, but that's okay; just make sure that one of the players with an extra card goes first.)
On your turn, reveal one card from your hand and place it face up in front of you. Select another player; that player must then announce how many cards he has in his hand that have at least one element in common with the revealed card. (It helps if that player also mentions how many total cards he has left in his hand.) That player then takes the next turn.
At any time (even out of turn), you may announce that you know what the card in the center of the table is. Write down what you think it is, then look at the card. If you were correct, you win! If not, place it back face-down without revealing what the card is, reveal all your remaining cards face-up in front of you, and the rest of the players continue playing. If it was your turn, choose another player to go next.
I invented this game in December 2003, as part of my continuing project to develop alternate Aquarius games. It was inspired by games like Clue, Sleuth, or especially Black Vienna.
Elementary as it currently stands is playable, but I'm not very happy with it. Brian Hanechak suggested a change that I think would help, but I still haven't tried it: when you select a player, that player must announce the total number of panels on cards in his hand that match panels on the revealed card. If you try this out, mail me and let me know how it works.