diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,10 @@
 and this project adheres to the
 [Haskell Package Versioning Policy](https://pvp.haskell.org/).
 
+## 0.2.1.0 - 2023-10-30
+
+* `Eq`, `Ord`, `Show`, `Applicative` and `Monad` instances
+
 ## 0.1.0.0 - 2023-03-15
 
-	Initial version
+Initial version
diff --git a/README.md b/README.md
--- a/README.md
+++ b/README.md
@@ -2,3 +2,15 @@
 
 A simple data structure helping us ask questions of the following
 sort: "does all this data have the same /BLANK/ and if so what is it?"
+
+For example:
+
+        doTheseHaveTheSameLength :: [String] -> String
+        doTheseHaveTheSameLength l = case foldMap (Somebody . length) of
+          Somebody n -> "They all have length " <> show n
+          Nobody     -> "The lengths differ"
+          Anybody    -> "You didn't give me any strings"
+
+This can of course be done with `Maybe (Maybe x)` instead, but doing
+so runs the risk of getting confused: which is `Nothing` and which is
+`Just Nothing`?
diff --git a/agreeing.cabal b/agreeing.cabal
--- a/agreeing.cabal
+++ b/agreeing.cabal
@@ -1,11 +1,11 @@
 cabal-version: 1.12
 
--- This file has been generated from package.yaml by hpack version 0.35.2.
+-- This file has been generated from package.yaml by hpack version 0.36.0.
 --
 -- see: https://github.com/sol/hpack
 
 name:           agreeing
-version:        0.2.0.0
+version:        0.2.1.0
 synopsis:       Idiomatic data structure for agreement
 description:    Please see the README on GitHub at <https://github.com/jcranch/agreeing#readme>
 category:       Data
diff --git a/src/Data/Agreement.hs b/src/Data/Agreement.hs
--- a/src/Data/Agreement.hs
+++ b/src/Data/Agreement.hs
@@ -9,6 +9,26 @@
 -- >   Somebody n -> "They all have length " <> show n
 -- >   Nobody     -> "The lengths differ"
 -- >   Anybody    -> "You didn't give me any strings"
+--
+-- This can of course be done with `Maybe (Maybe x)` instead, but
+-- doing so runs the risk of getting confused: which is `Nothing` and
+-- which is `Just Nothing`?
+--
+-- Unfortunately, there are two `Applicative` instances.
+--
+-- One is easy to motivate intrinsically. If we think of `Anybody` as
+-- an empty list, `Somebody` as a singleton list, and `Nobody` as a
+-- multi-element list, and think of the applicative instance on as
+-- corresponding to the cartesian product, then we get an
+-- `Applicative` instance with
+--
+-- > Anybody <*> Anybody = Anybody
+-- > Anybody <*> Nobody = Nobody
+--
+-- This however cannot possibly correspond to a `Monad` instance (if
+-- the first argument of `>>=` is Anybody, there's no way of
+-- inspecting the second). We thus choose another, which does.
+
 module Data.Agreement (
   Agreement(..),
   getSomebody,
@@ -25,6 +45,7 @@
 --
 --   * `Anybody` is a failure to make any choice.
 data Agreement a = Anybody | Somebody a | Nobody
+  deriving (Eq, Ord, Show)
 
 -- | This picks out consistent choices as `Just`.
 getSomebody :: Agreement a -> Maybe a
@@ -32,18 +53,34 @@
 getSomebody _ = Nothing
 
 instance Functor Agreement where
-  fmap _ Anybody = Anybody
+  fmap _ Anybody      = Anybody
   fmap f (Somebody x) = Somebody (f x)
-  fmap _ Nobody = Nobody
+  fmap _ Nobody       = Nobody
 
+-- | Not the only possible instance: see introduction
+instance Applicative Agreement where
+  pure = Somebody
+  Nobody     <*> _ = Nobody
+  Anybody    <*> _ = Anybody
+  Somebody f <*> x = f <$> x
+  liftA2 _ Nobody       _ = Nobody
+  liftA2 _ Anybody      _ = Anybody
+  liftA2 f (Somebody x) y = f x <$> y
+
+instance Monad Agreement where
+  return = pure
+  Nobody     >>= _ = Nobody
+  Anybody    >>= _ = Anybody
+  Somebody x >>= f = f x
+
 instance (Eq a) => Semigroup (Agreement a) where
-  Anybody <> x = x
-  Nobody <> _ = Nobody
-  Somebody x <> Anybody = Somebody x
-  Somebody _ <> Nobody = Nobody
+  Nobody     <> _          = Nobody
+  Anybody    <> x          = x
+  Somebody _ <> Nobody     = Nobody
+  Somebody x <> Anybody    = Somebody x
   Somebody x <> Somebody y
-    | x == y = Somebody x
-    | otherwise = Nobody
+    | x == y               = Somebody x
+    | otherwise            = Nobody
   stimes = stimesIdempotentMonoid
 
 instance (Eq a) => Monoid (Agreement a) where