diff --git a/src/main/lemondronor/circlebot.cljs b/src/main/lemondronor/circlebot.cljs
index 75651cd..d4fcb0d 100644
--- a/src/main/lemondronor/circlebot.cljs
+++ b/src/main/lemondronor/circlebot.cljs
@@ -274,7 +274,7 @@
 
 (def description-templates
   (map generation/parse-template
-       [(str "[{registration}|{registration}, a {type},|{militaryregistration}, a military aircraft,|"
+       [(str "[{registration}|{registration}, {type|a-an},|{militaryregistration}, a military aircraft,|"
              "{militaryregistration}, a military {type},|"
              "Aircraft with unknown registration, ICAO {icao}|"
              "Military aircraft with unknown registration, ICAO {militaryicao}] "
diff --git a/src/main/lemondronor/circlebot/generation.cljc b/src/main/lemondronor/circlebot/generation.cljc
index 5024cbe..526d4f9 100644
--- a/src/main/lemondronor/circlebot/generation.cljc
+++ b/src/main/lemondronor/circlebot/generation.cljc
@@ -14,7 +14,7 @@
     sequence = <'['> term+ <']'>
     optional = <'⁇'> no-ws-term
     choice = <'['> pattern <'|'> pattern (<'|'> pattern)* <']'>
-    varref = <'{'> #'[a-zA-Z\\_][a-zA-Z0-9\\-\\_\\.]+' <'}'>
+    varref = <'{'> #'[a-zA-Z\\_][a-zA-Z0-9\\-\\_\\.\\|]+' <'}'>
     text = #'[^\\{\\[\\]\\|⁇]+'
     no-ws-text = #'[^\\{\\[\\]\\|⁇\\s]+'
 "))
@@ -55,12 +55,43 @@
 ;;       '()
 ;;       (list {:varrefs [var] :text (str (data var))}))))
 
+(def vowels #{"a" "e" "i" "o" "u"})
+
+(defn is-consonant? [c]
+  (not (vowels (string/lower-case c))))
+
+(defn starts-with-consonant? [s]
+  (is-consonant? (subs s 0 1)))
+
+
+(def filters
+  {:a-an (fn a-an [s]
+           (if (starts-with-consonant? s)
+             (str "a " s)
+             (str "an " s)))})
+
+
+(defn apply-filter [s filter-name]
+  (if (nil? filter-name)
+    s
+    (let [filter (filters (keyword filter-name))]
+      (when-not filter
+        (throw (js/Error. (str "Unknown filter: " filter-name))))
+      (filter s))))
+
+
+(defn parse-varref [s]
+  (let [[var filter] (string/split s #"\|" 2)]
+    {:var (keyword var) :filter filter}))
+
+
 (defmethod expand% :varref [template data]
-  (let [var (keyword (second template))
+  (let [varref (second template)
+        {:keys [var filter]} (parse-varref varref)
         val (data var)]
     (if (or (nil? val) (= val ""))
       '()
-      (list {:varrefs [var] :text (str (data var))}))))
+      (list {:varrefs [var] :text (apply-filter (str (data var)) filter)}))))
 
 (defmethod expand% :text [template data]
   (list {:varrefs [] :text (second template)}))
diff --git a/src/test/lemondronor/circlebot/generation_test.cljs b/src/test/lemondronor/circlebot/generation_test.cljs
index afa0101..4873cbb 100644
--- a/src/test/lemondronor/circlebot/generation_test.cljs
+++ b/src/test/lemondronor/circlebot/generation_test.cljs
@@ -66,12 +66,28 @@
                 :locality 2})))))
 
 
-(deftest var-paths
-  (is (= "Hello, John"
-         (generation/generate
-          [(generation/parse-template "Hello, {person.name}")]
-          {:person {:name "John"}})))
-  (is (= 9
-         (generation/generate
-          [(generation/parse-template "Hello, {person.name}")]
-          {:person {:age 49}}))))
+(deftest is-consonant
+  (is (generation/is-consonant? "f"))
+  (is (generation/is-consonant? "F"))
+  (is (not (generation/is-consonant? "a")))
+  (is (not (generation/is-consonant? "A"))))
+
+
+(deftest filters
+  (let [templates [(generation/parse-template "It is {thing|a-an}")]]
+    (is (= "It is a bird"
+           (generation/generate templates {:thing "bird"})))
+    (is (= "It is an animal"
+           (generation/generate templates {:thing "animal"})))
+    (is (= "It is an Animal"
+           (generation/generate templates {:thing "Animal"})))))
+
+;; (deftest var-paths
+;;   (is (= "Hello, John"
+;;          (generation/generate
+;;           [(generation/parse-template "Hello, {person.name}")]
+;;           {:person {:name "John"}})))
+;;   (is (= 9
+;;          (generation/generate
+;;           [(generation/parse-template "Hello, {person.name}")]
+;;           {:person {:age 49}}))))
diff --git a/src/test/lemondronor/circlebot_test.cljs b/src/test/lemondronor/circlebot_test.cljs
index 81fb406..9ac125b 100644
--- a/src/test/lemondronor/circlebot_test.cljs
+++ b/src/test/lemondronor/circlebot_test.cljs
@@ -24,6 +24,7 @@
            {:icao "71BE34"
             :registration "HL7634"
             :callsign nil
+            :type "A388"
             :lon -118.416438
             :lat 33.937908
             :alt 100
@@ -98,5 +99,8 @@
     (is (re-find #"military" (-> (circlebot/expand-template data) :text))))
   (let [data {:locality "Palmdale", :continent "North America", :military? true, :alt 3200, :speed "161", :normalized-curviness 15.783422690487765, :accuracy "centroid", :country_a "USA", :continent_gid "whosonfirst:continent:102191575", :name "Palmdale", :squawk "5330", :icao "AE1482", :county_a "LO", :county "Los Angeles County", :source "whosonfirst", :gid "whosonfirst:locality:85923493", :curviness 1098.803548060181, :locality_gid "whosonfirst:locality:85923493", :region "California", :militaryicao "AE1482", :region_a "CA", :nearbydistance 7.828, :callsign "RAIDR49", :layer "locality", :mlat? false, :country_gid "whosonfirst:country:85633793", :label "Palmdale, CA, USA", :id "85923493", :lon -118.049183, :region_gid "whosonfirst:region:85688637", :lat 34.649808, :militaryregistration "166765", :county_gid "whosonfirst:county:102086957", :started-circling-time 1576267564959, :distance 6.336, :source_id "85923493", :registration "166765", :confidence 0.5, :country "United States", :postime 1576267555709, :nearbylandmark "Living Faith Foursquare Church"}]
     (is (re-find #"military" (-> (circlebot/expand-template data) :text))))
-
-  )
+  (testing "a vs. an for type"
+    (let [data {:registration "TEST" :type "Airbus 380" :locality "Test City"}]
+      (is (re-find #"an Airbus" (:text (circlebot/expand-template data)))))
+    (let [data {:registration "TEST" :type "Yoyo 380" :locality "Test City"}]
+      (is (re-find #"a Yoyo" (:text (circlebot/expand-template data)))))))