What’s the difference between “validate” and “validates”?

validates This method is a shortcut to all default validators and any custom validator classes ending in ‘Validator’. Note that Rails default validators can be overridden inside specific classes by creating custom validator classes in their place such as PresenceValidator.

validates :title, :body, :presence => true

validate, Adds a validation method or block to the class. This is useful when overriding the validate instance method becomes too unwieldy and you’re looking for more descriptive declaration of your validations.

validate :must_be_friends

  def must_be_friends
    errors.add(:base, 'Must be friends to leave a comment') unless commenter.friend_of?(commentee)
  end