diff --git a/spacy/kb.pxd b/spacy/kb.pxd
index e715cad88..9d9a21a8c 100644
--- a/spacy/kb.pxd
+++ b/spacy/kb.pxd
@@ -3,8 +3,7 @@ from cymem.cymem cimport Pool
 from preshed.maps cimport PreshMap
 from libcpp.vector cimport vector
 from libc.stdint cimport int32_t, int64_t
-from .typedefs cimport attr_t, hash_t
-from .strings cimport hash_string
+from .typedefs cimport hash_t
 
 
 # Internal struct, for storage and disambiguation. This isn't what we return
@@ -68,26 +67,10 @@ cdef class KnowledgeBase:
     # efficient.
     cdef object _aliases_table
 
-    def __len__(self):
-        return self._entries.size()
-
-    def add_entity(self, name, float prob, vectors=None, features=None, aliases=None):
-        # TODO: more friendly check for non-unique name
-        if name in self:
-            return
-
-        cdef hash_t key = hash_string(name)
-        self.c_add_entity(key, prob, self._vectors_table.get_pointer(vectors),
-                   self._features_table.get(features))
-
-        # TODO: hash the aliases?
-        for alias, prob_alias in aliases:
-            self._aliases_table.add(alias, key, prob_alias)
-
     cdef void c_add_entity(self, hash_t key, float prob, const int32_t* vector_rows,
                     int feats_row) nogil:
         """Add an entry to the knowledge base."""
-        # This is what we'll map the orth to. It's where the entry will sit
+        # This is what we'll map the hash key to. It's where the entry will sit
         # in the vector of entries, so we can get it later.
         cdef int64_t index = self._entries.size()
         self._entries.push_back(
diff --git a/spacy/kb.pyx b/spacy/kb.pyx
new file mode 100644
index 000000000..ce76f2fc4
--- /dev/null
+++ b/spacy/kb.pyx
@@ -0,0 +1,27 @@
+from .strings cimport hash_string
+
+
+cdef class KnowledgeBase:
+    def __len__(self):
+        return self._entries.size()
+
+    def add_entity(self, name, float prob, vectors=None, features=None, aliases=None):
+        # TODO: more friendly check for non-unique name
+        if name in self:
+            return
+
+        cdef hash_t name_hash = hash_string(name)
+        self.c_add_entity(name_hash, prob, self._vectors_table.get_pointer(vectors),
+                   self._features_table.get(features))
+
+    def add_alias(self, alias, entities, probabilities):
+        """For a given alias, add its potential entities and prior probabilies to the KB."""
+        cdef hash_t alias_hash = hash_string(alias)
+
+        # TODO: check len(entities) == len(probabilities)
+        for entity, prob in zip(entities, probabilities):
+            cdef hash_t entity_hash = hash_string(entity)
+            cdef int64_t entity_index = self._index[entity_hash]
+            # TODO: check that entity is already in this KB (entity_index is OK)
+            self._aliases_table.add(alias_hash, entity_index, prob)
+