Undue influence consists:

1. (1) In the use, by one in whom a confidence is reposed by another, or who holds a real or apparent authority over him, of such confidence or authority for the purpose of obtaining an unfair advantage over him; or
2. (2) In taking an unfair advantage of another's weakness of mind; or
3. (3) In taking a grossly oppressive and unfair advantage of another's necessities or distress.

Source: CivC 1877, § 886; CL 1887, § 3510; RCivC 1903, § 1204; RC 1919, § 819; SDC 1939, § 10.0310.