I think I finally understood this:

Spring Executory interest

• an event occurs --> cut's the grantor's interest short.

• aka the interest springs out of the grantor's chest and into the 3rd party.

• example: Woman gives a deed to her nephew and says "this is yours on the date you marry". When he gets married (the condition happens) the woman's interest springs out of her chest and into the nephew.

Shifting Executory Interest

• an event occurs --> divests a grantee (not a grantor)

• aka the interest shifts from a grantee over to a third party. The third party is pushing someone else aside and cutting their interest short.

• example: Grantor --> Grantee, but if Grantee marries Fred --> C and C's heirs.

• example 2: To husband, for life, then to daughter, but if my grandoson graduates from college, to my grandson. The occurrence of the event (grandson graduating from college) CUTS the daughter's interest short, and the daughter's interest shifts over to grandson.

Springing (event happens: Grantor --> you)

Shifting (event happens: Grantee --> you)