Deduction is rigid, which makes it difficult to incorporate into board games, which thrive best in the rivers of uncertainty and doubt. If a deduction problem can be solved, it can be solved absolutely, at which point it simply becomes a matter of figuring out what the solution is. I love such puzzles but I also understand that they easily fail in the context of a board game.

The Search For Planet X, by Ben Rosset and Matthew O’Malley, might be just about as good of a deduction game as can be made. It understands the limitations of the genre and does its best to mitigate them as much as possible. Because it’s so good at what it does, I’m more convinced than ever that a game centered around pure deduction can only reach a certain level of greatness—a high peak, but below the potential of other games. At the end of the day there has to be an objectively true, fully comprehensible solution, and you’ve either got it or you don’t.
Where great deduction games like Planet X or The Shipwreck Arcana succeed is in the non-certain elements. As Greg Costikyan comments in Uncertainty in Games, “games require uncertainty to hold our interest, and…the struggle to master uncertainty is central to the appeal of games”.
He does identify “Solver’s Uncertainty” as one potential source of uncertainty, but I agree with him that games that focus on puzzles tend to be both artificial and limiting of creativity. He also rightly points out that puzzle solving is embedded in nearly every game, but in less rigid ways:
“Almost any multivariable strategy game creates puzzles, but these puzzles, unlike those of explicit puzzle games, emerge from the complexity of the mechanics of the game itself”.

The Shipwreck Arcana capitalizes on emergent complexity by creating situations where teammates have to guess and second-guess how much their counterparts understand the complexities of the situation and how much that understanding informs their clues. Planet X creates those fuzzy edges on the periphery of the central deduction puzzle in a couple of ways.
First, it challenges you to ask the right questions. Everyone is searching for the slippery Planet X, which must live in one of the 18 segments of the sky. Four other bodies live in the sky, each following their own rules: dwarf planets, asteroids, gas clouds, and comets. A few of the spaces are empty. You’ve got three tools for discovering where everything is located: you can target an area and simply learn what’s there (planet X “appearing empty” in this search); you can survey a wedge of the sky, searching for one type of stellar body and learning how many exist in said wedge; or you can research and learn a new rule, like, “no asteroids appear within two spaces of a gas cloud”.
These are your tools and you must use them to discover knowledge as quickly as possible. Planet X uses a time track to valuate each action. Targeting costs 4 time, for instance, while research only costs 1. Whoever has spent the fewest amount of time gets initiative. After a game or two you’ll discover some simple tricks to survey more effectively. For instance, the survey action gets more expensive as you narrow the band of your surveillance. But if you overlap areas you want to search with a segment you already know is void of that thing you can effectively conduct a narrow search without the increased price.
The second way Planet X pushes beyond cut and dry deduction is by allowing you to get clues about what your opponents are doing. You know which questions they’re asking, for instance. On more than one occasion I’ve been baffled at the survey Amber just initiated given what I thought I knew about what she knew, and had to return to my notes, wondering if she gained a specific insight through a lucky early guess.
You also periodically get the opportunity to submit theories regarding the location of the lesser bodies. If you’ve played Alchemists you understand how disruptive this can be. The penalty for submitting an incorrect theory is much less severe than the profit from submitting a correct one, so there’s always a temptation to go for it if you have a hunch. But you get to see in which segments others have placed their guesses, which means that you know they don’t think that space is empty (at the very least). But do they know that space isn’t empty, or are they merely making an educated guess like you are? How much are you willing to stake on that information?

I’ve found that if you’re going for straight deduction, not submitting any answers until you know for sure that you’re correct, the game plays out more or less the same each time. The optimal amount of time needed to simply get the quantity of information needed to deduce the answer can be approached. To compete past that, to push further, you’ve got to be okay with some doubt and risk spectacular failure. I don’t know if I’ll try to push the game that hard, however. I like the puzzle solving. I don’t want to discover 30 minutes into a 60 minute game that everything I thought I knew was wrong and then be stuck trying to untangle the web of assumptions I made to get to that place.
Then again, maybe this will be the next challenge once the puzzle gets stale. I don’t mean the guesswork, but the notetaking. I’ve figured out a very clean notation system, which is its own reward (it feels so scientific!), but what if I developed a great system for tracking nested assumptions and people-reading notes? Would that slow the game down too much, or reveal new depths? Would I actually gain any new information?
Or perhaps I should be content with what I plainly have: a superior deduction game that presents a satisfying puzzle. A puzzle that always demands genuine thought without ever becoming frustratingly obtuse or difficult. It’s a good thing to have. When I solved for (planet) X in my first game I jumped up from my chair in excitement. Can deduction games improve on The Search for Planet X without becoming something else entirely?