diff --git a/question/behaviour/behaviourbase.php b/question/behaviour/behaviourbase.php
index 97bcde81617..24a69157afb 100644
--- a/question/behaviour/behaviourbase.php
+++ b/question/behaviour/behaviourbase.php
@@ -628,7 +628,7 @@ abstract class question_behaviour_with_save extends question_behaviour {
 
 /**
  * This helper class contains the constants and methods required for
- * manipulating scores for certainly based marking.
+ * manipulating scores for certainty based marking.
  *
  * @copyright  2009 The Open University
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
@@ -665,10 +665,10 @@ abstract class question_cbm {
     }
 
     /**
-     * Given a fraction, and a certainly, compute the adjusted fraction.
+     * Given a fraction, and a certainty, compute the adjusted fraction.
      * @param number $fraction the raw fraction for this question.
-     * @param int $certainty one of the certainly level constants.
-     * @return number the adjusted fraction taking the certainly into account.
+     * @param int $certainty one of the certainty level constants.
+     * @return number the adjusted fraction taking the certainty into account.
      */
     public static function adjust_fraction($fraction, $certainty) {
         return self::$offset[$certainty] + self::$factor[$certainty] * $fraction;
@@ -676,7 +676,7 @@ abstract class question_cbm {
 
     /**
      * @param int $certainty one of the LOW/MED/HIGH constants.
-     * @return string a textual desciption of this certainly.
+     * @return string a textual description of this certainty.
      */
     public static function get_string($certainty) {
         return get_string('certainty' . $certainty, 'qbehaviour_deferredcbm');
diff --git a/question/behaviour/deferredcbm/behaviour.php b/question/behaviour/deferredcbm/behaviour.php
index af487eaed64..e5464fa1cc0 100644
--- a/question/behaviour/deferredcbm/behaviour.php
+++ b/question/behaviour/deferredcbm/behaviour.php
@@ -16,7 +16,7 @@
 
 /**
  * Question behaviour that is like the deferred feedback model, but with
- * certainly based marking. That is, in addition to the other controls, there are
+ * certainty based marking. That is, in addition to the other controls, there are
  * where the student can indicate how certain they are that their answer is right.
  *
  * @package    qbehaviour
diff --git a/question/behaviour/deferredcbm/renderer.php b/question/behaviour/deferredcbm/renderer.php
index 8cb33d42ca4..25d3d727359 100644
--- a/question/behaviour/deferredcbm/renderer.php
+++ b/question/behaviour/deferredcbm/renderer.php
@@ -36,7 +36,7 @@ defined('MOODLE_INTERNAL') || die();
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
 class qbehaviour_deferredcbm_renderer extends qbehaviour_renderer {
-    protected function certainly_choices($controlname, $selected, $readonly) {
+    protected function certainty_choices($controlname, $selected, $readonly) {
         $attributes = array(
             'type' => 'radio',
             'name' => $controlname,
@@ -64,7 +64,7 @@ class qbehaviour_deferredcbm_renderer extends qbehaviour_renderer {
 
     public function controls(question_attempt $qa, question_display_options $options) {
         return html_writer::tag('div', get_string('howcertainareyou', 'qbehaviour_deferredcbm',
-                $this->certainly_choices($qa->get_behaviour_field_name('certainty'),
+                $this->certainty_choices($qa->get_behaviour_field_name('certainty'),
                 $qa->get_last_behaviour_var('certainty'), $options->readonly)),
                 array('class' => 'certaintychoices'));
     }
diff --git a/question/behaviour/immediatecbm/behaviour.php b/question/behaviour/immediatecbm/behaviour.php
index add1388f044..3e0a12256a4 100644
--- a/question/behaviour/immediatecbm/behaviour.php
+++ b/question/behaviour/immediatecbm/behaviour.php
@@ -34,10 +34,10 @@ require_once(dirname(__FILE__) . '/../immediatefeedback/behaviour.php');
  * Question behaviour for immediate feedback with CBM.
  *
  * Each question has a submit button next to it along with some radio buttons
- * to input a certainly, that is, how sure they are that they are right.
+ * to input a certainty, that is, how sure they are that they are right.
  * The student can submit their answer at any time for immediate feedback.
  * Once the qustion is submitted, it is not possible for the student to change
- * their answer any more. The student's degree of certainly affects their score.
+ * their answer any more. The student's degree of certainty affects their score.
  *
  * @copyright  2009 The Open University
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
diff --git a/question/behaviour/missing/behaviour.php b/question/behaviour/missing/behaviour.php
index 0c3e31f26fb..a1e607c1f76 100644
--- a/question/behaviour/missing/behaviour.php
+++ b/question/behaviour/missing/behaviour.php
@@ -33,7 +33,7 @@ defined('MOODLE_INTERNAL') || die();
  * is not available.
  *
  * Imagine, for example, that a quiz attempt has been restored from another
- * Moodle site with more behaviours installed, or an behaviour
+ * Moodle site with more behaviours installed, or a behaviour
  * that used to be available in this site has been uninstalled. Obviously all we
  * can do is have some code to prevent fatal errors.
  *
diff --git a/question/engine/lib.php b/question/engine/lib.php
index 9a6ad903846..88c0065d418 100644
--- a/question/engine/lib.php
+++ b/question/engine/lib.php
@@ -189,7 +189,7 @@ abstract class question_engine {
     }
 
     /**
-     * Create an behaviour for a particular type. If that type cannot be
+     * Create a behaviour for a particular type. If that type cannot be
      * found, return an instance of qbehaviour_missing.
      *
      * Normally you should use {@link make_archetypal_behaviour()}, or
@@ -239,7 +239,7 @@ abstract class question_engine {
     }
 
     /**
-     * Create an behaviour for a particular type. If that type cannot be
+     * Create a behaviour for a particular type. If that type cannot be
      * found, return an instance of qbehaviour_missing.
      *
      * Normally you should use {@link make_archetypal_behaviour()}, or
@@ -394,7 +394,7 @@ abstract class question_engine {
     }
 
     /**
-     * Get the translated name of an behaviour, for display in the UI.
+     * Get the translated name of a behaviour, for display in the UI.
      * @param string $behaviour the internal name of the model.
      * @return string name from the current language pack.
      */
diff --git a/question/engine/questionattemptstep.php b/question/engine/questionattemptstep.php
index d2174e24cb6..7f7e238af68 100644
--- a/question/engine/questionattemptstep.php
+++ b/question/engine/questionattemptstep.php
@@ -295,7 +295,7 @@ class question_attempt_step {
     }
 
     /**
-     * @param string $name the name of an behaviour variable to look for in the submitted data.
+     * @param string $name the name of a behaviour variable to look for in the submitted data.
      * @return bool whether a variable with this name exists in the question type data.
      */
     public function has_behaviour_var($name) {
@@ -303,7 +303,7 @@ class question_attempt_step {
     }
 
     /**
-     * @param string $name the name of an behaviour variable to look for in the submitted data.
+     * @param string $name the name of a behaviour variable to look for in the submitted data.
      * @return string the requested variable, or null if the variable is not set.
      */
     public function get_behaviour_var($name) {
diff --git a/question/type/questionbase.php b/question/type/questionbase.php
index e4566fac615..042afb5a86a 100644
--- a/question/type/questionbase.php
+++ b/question/type/questionbase.php
@@ -154,7 +154,7 @@ abstract class question_definition {
      * one asked for. For example, you migth want to return a
      * qbehaviour_interactive_adapted_for_myqtype.
      *
-     * @param question_attempt $qa the attempt we are creating an behaviour for.
+     * @param question_attempt $qa the attempt we are creating a behaviour for.
      * @param string $preferredbehaviour the requested type of behaviour.
      * @return question_behaviour the new behaviour object.
      */