diff --git a/activemodel/lib/active_model/validations.rb b/activemodel/lib/active_model/validations.rb
index 718fc78605..1116f6b8ee 100644
--- a/activemodel/lib/active_model/validations.rb
+++ b/activemodel/lib/active_model/validations.rb
@@ -68,8 +68,9 @@ module ActiveModel
#
# Options:
# * :on - Specifies the contexts where this validation is active.
- # You can pass a symbol or an array of symbols.
- # (e.g. on: :create or on: :custom_validation_context or
+ # Runs in all validation contexts by default (nil). You can pass a symbol
+ # or an array of symbols. (e.g. on: :create or
+ # on: :custom_validation_context or
# on: [:create, :custom_validation_context])
# * :allow_nil - Skip validation if attribute is +nil+.
# * :allow_blank - Skip validation if attribute is blank.
@@ -130,8 +131,9 @@ module ActiveModel
#
# Options:
# * :on - Specifies the contexts where this validation is active.
- # You can pass a symbol or an array of symbols.
- # (e.g. on: :create or on: :custom_validation_context or
+ # Runs in all validation contexts by default (nil). You can pass a symbol
+ # or an array of symbols. (e.g. on: :create or
+ # on: :custom_validation_context or
# on: [:create, :custom_validation_context])
# * :if - Specifies a method, proc or string to call to determine
# if the validation should occur (e.g. if: :allow_validation,
diff --git a/activemodel/lib/active_model/validations/validates.rb b/activemodel/lib/active_model/validations/validates.rb
index ae8d377fdf..bda436d8d0 100644
--- a/activemodel/lib/active_model/validations/validates.rb
+++ b/activemodel/lib/active_model/validations/validates.rb
@@ -71,9 +71,11 @@ module ActiveModel
#
# There is also a list of options that could be used along with validators:
#
- # * :on - Specifies when this validation is active. Runs in all
- # validation contexts by default (+nil+), other options are :create
- # and :update.
+ # * :on - Specifies the contexts where this validation is active.
+ # Runs in all validation contexts by default (nil). You can pass a symbol
+ # or an array of symbols. (e.g. on: :create or
+ # on: :custom_validation_context or
+ # on: [:create, :custom_validation_context])
# * :if - Specifies a method, proc or string to call to determine
# if the validation should occur (e.g. if: :allow_validation,
# or if: Proc.new { |user| user.signup_step > 2 }). The method,
diff --git a/activemodel/lib/active_model/validations/with.rb b/activemodel/lib/active_model/validations/with.rb
index ff41572105..a2531327bf 100644
--- a/activemodel/lib/active_model/validations/with.rb
+++ b/activemodel/lib/active_model/validations/with.rb
@@ -52,8 +52,11 @@ module ActiveModel
# end
#
# Configuration options:
- # * :on - Specifies when this validation is active
- # (:create or :update).
+ # * :on - Specifies the contexts where this validation is active.
+ # Runs in all validation contexts by default (nil). You can pass a symbol
+ # or an array of symbols. (e.g. on: :create or
+ # on: :custom_validation_context or
+ # on: [:create, :custom_validation_context])
# * :if - Specifies a method, proc or string to call to determine
# if the validation should occur (e.g. if: :allow_validation,
# or if: Proc.new { |user| user.signup_step > 2 }).
diff --git a/activerecord/lib/active_record/validations/associated.rb b/activerecord/lib/active_record/validations/associated.rb
index b4785d3ba4..47ccef31a5 100644
--- a/activerecord/lib/active_record/validations/associated.rb
+++ b/activerecord/lib/active_record/validations/associated.rb
@@ -29,9 +29,11 @@ module ActiveRecord
# Configuration options:
#
# * :message - A custom error message (default is: "is invalid").
- # * :on - Specifies when this validation is active. Runs in all
- # validation contexts by default (+nil+), other options are :create
- # and :update.
+ # * :on - Specifies the contexts where this validation is active.
+ # Runs in all validation contexts by default (nil). You can pass a symbol
+ # or an array of symbols. (e.g. on: :create or
+ # on: :custom_validation_context or
+ # on: [:create, :custom_validation_context])
# * :if - Specifies a method, proc or string to call to determine
# if the validation should occur (e.g. if: :allow_validation,
# or if: Proc.new { |user| user.signup_step > 2 }). The method,
diff --git a/activerecord/lib/active_record/validations/presence.rb b/activerecord/lib/active_record/validations/presence.rb
index e586744818..c7aa814ba8 100644
--- a/activerecord/lib/active_record/validations/presence.rb
+++ b/activerecord/lib/active_record/validations/presence.rb
@@ -44,9 +44,11 @@ module ActiveRecord
#
# Configuration options:
# * :message - A custom error message (default is: "can't be blank").
- # * :on - Specifies when this validation is active. Runs in all
- # validation contexts by default (+nil+), other options are :create
- # and :update.
+ # * :on - Specifies the contexts where this validation is active.
+ # Runs in all validation contexts by default (nil). You can pass a symbol
+ # or an array of symbols. (e.g. on: :create or
+ # on: :custom_validation_context or
+ # on: [:create, :custom_validation_context])
# * :if - Specifies a method, proc or string to call to determine if
# the validation should occur (e.g. if: :allow_validation, or
# if: Proc.new { |user| user.signup_step > 2 }). The method, proc