The President's power to promulgate ordinances under Article 123 is a legislative power exercised when Parliament is not in session. Ordinances can amend existing laws, including Central Acts, provided the subject matter falls within the legislative competence of Parliament. They can also be given retrospective effect, meaning they can come into force from a date prior to their promulgation. However, an ordinance cannot contain provisions which Parliament cannot enact, which includes provisions that would violate fundamental rights. Therefore, an ordinance cannot abridge a Fundamental Right.