Explanation:

- The distinction between formal sources (those that give laws their legal validity, like legislation and precedents) and material sources (those from which the substance of the rules is derived, like customs or historical documents) is a well-known classification in legal theory.

- Option 1: Salmond

- Correct Answer

- Salmond, a prominent jurist, is famous for dividing sources of law into formal and material sources.

- Option 2: Paton

- Paton contributed to legal theory but is not specifically associated with this distinction.

- Option 3: Allen

- Allen discussed sources of law, but did not formally classify them as Salmond did.

- Option 4: Austin

- Austin focused mainly on command theory and sources of law but did not make this specific division.

Correct Answer: Option 1 - Salmond