diff --git a/src/ideaCollisionGenerator.py b/src/ideaCollisionGenerator.py
index 406ac5f..6c98bcd 100644
--- a/src/ideaCollisionGenerator.py
+++ b/src/ideaCollisionGenerator.py
@@ -3,27 +3,34 @@
 import os
 
 class IdeaCollisionGenerator:
-    def __init__(self):
+    def __init__(self, numKeywords=10):
+        # keywords are matched in pairs, so the count has to be even
+        if numKeywords < 2 or numKeywords % 2 != 0:
+            raise ValueError("numKeywords must be a positive even number")
+        self.numKeywords = numKeywords
         self.keywords = []
         self.pairs = []
         self.ideas = []
 
+    def ordinal(self, n):
+        # 1st, 2nd, 3rd, 4th ... 11th, 12th, 13th ... 21st, 22nd, 23rd
+        if n % 100 in (11, 12, 13):
+            suffix = "th"
+        elif n % 10 == 1:
+            suffix = "st"
+        elif n % 10 == 2:
+            suffix = "nd"
+        elif n % 10 == 3:
+            suffix = "rd"
+        else:
+            suffix = "th"
+        return str(n) + suffix
+
     def getKeywords(self):
-        # get 10 keywords from user
-        numKeywords = 10
-        for i in range(numKeywords):
-            if i == 0:
-                keyword = input("Enter 1st keyword: ")
-                self.keywords.append(keyword)
-            elif i == 1:
-                keyword = input("Enter 2nd keyword: ")
-                self.keywords.append(keyword)
-            elif i == 2:
-                keyword = input("Enter 3rd keyword: ")
-                self.keywords.append(keyword)
-            else:
-                keyword = input("Enter " + str(i+1) + "th keyword: ")
-                self.keywords.append(keyword)
+        # get keywords from user
+        for i in range(self.numKeywords):
+            keyword = input("Enter " + self.ordinal(i+1) + " keyword: ")
+            self.keywords.append(keyword)
 
         # randomize keywords
         random.shuffle(self.keywords)
diff --git a/tests/test_ideaCollisionGenerator.py b/tests/test_ideaCollisionGenerator.py
index 9d8cbf2..22ada0f 100644
--- a/tests/test_ideaCollisionGenerator.py
+++ b/tests/test_ideaCollisionGenerator.py
@@ -38,6 +38,41 @@ def recordingInput(prompt):
         self.assertEqual(prompts[3], "Enter 4th keyword: ")
         self.assertEqual(prompts[9], "Enter 10th keyword: ")
 
+    def testPromptsAreCorrectPastTwenty(self):
+        generator = IdeaCollisionGenerator(numKeywords=24)
+        prompts = []
+
+        def recordingInput(prompt):
+            prompts.append(prompt)
+            return "keyword"
+
+        with mock.patch("builtins.input", recordingInput):
+            with mock.patch("random.shuffle"):
+                generator.getKeywords()
+
+        self.assertEqual(prompts[20], "Enter 21st keyword: ")
+        self.assertEqual(prompts[21], "Enter 22nd keyword: ")
+        self.assertEqual(prompts[22], "Enter 23rd keyword: ")
+
+    def testKeywordCountIsConfigurable(self):
+        generator = IdeaCollisionGenerator(numKeywords=4)
+        with mock.patch("builtins.input", side_effect=["a", "b", "c", "d"]):
+            with mock.patch("random.shuffle"):
+                generator.getKeywords()
+        self.assertEqual(generator.keywords, ["a", "b", "c", "d"])
+
+    def testKeywordCountDefaultsToTen(self):
+        self.assertEqual(IdeaCollisionGenerator().numKeywords, 10)
+
+    def testOddKeywordCountIsRejected(self):
+        # createPairs() needs an even count, so it is refused up front
+        with self.assertRaises(ValueError):
+            IdeaCollisionGenerator(numKeywords=3)
+
+    def testNonPositiveKeywordCountIsRejected(self):
+        with self.assertRaises(ValueError):
+            IdeaCollisionGenerator(numKeywords=0)
+
     def testKeywordsAreShuffled(self):
         generator = IdeaCollisionGenerator()
         with mock.patch("builtins.input", side_effect=[str(i) for i in range(10)]):
@@ -54,6 +89,19 @@ def testEmptyKeywordsAreAccepted(self):
         self.assertEqual(generator.keywords, [""] * 10)
 
 
+class TestOrdinal(unittest.TestCase):
+    def testSuffixes(self):
+        generator = IdeaCollisionGenerator()
+        expected = {
+            1: "1st", 2: "2nd", 3: "3rd", 4: "4th", 10: "10th",
+            11: "11th", 12: "12th", 13: "13th", 14: "14th",
+            21: "21st", 22: "22nd", 23: "23rd", 24: "24th",
+            101: "101st", 111: "111th", 112: "112th", 113: "113th", 121: "121st",
+        }
+        for n, text in expected.items():
+            self.assertEqual(generator.ordinal(n), text)
+
+
 class TestCreatePairs(unittest.TestCase):
     def testPairsAdjacentKeywords(self):
         generator = IdeaCollisionGenerator()