A more thorough explanation:

ex necessitate

Ex necessitate means "of or from necessity." It is often used to describe something that is required or necessary because of a particular situation or circumstance.

• Ex necessitate legis: This means "from the necessity of the law." For example, a person may be required to pay taxes because of the law.
• Ex necessitate rei: This means "from the necessity or urgency of the thing or case." For example, a doctor may need to perform emergency surgery because it is necessary to save a patient's life.

These examples illustrate how ex necessitate is used to describe something that is required or necessary because of a particular situation or circumstance.