This is part 2 of the series. The first part of the series can be found here (link). The first part discussed the true doctrine of the knowledge of God, but this section defines the erroneous doctrine of middle knowledge and describes its history. As is discussed in the video, Molinism was the brainchild of Lessius, Fonseca, and/or Molina (three Jesuits who couldn't decide among themselves who invented the doctrine) in opposition to Dominicans who held to a view of free will that is similar to that of Calvinists.
The Jesuits were seeking to make God's election to be based on foreseen faith and good works, as well as to defend their view of man's free will as autonomous. The only way they saw around the Dominicans' observation that God's will consists of natural and free knowledge was to invent a third category of knowledge that they designated "middle knowledge."
This "middle knowledge" is allegedly different from natural knowledge in that it is indeterminate, not being based on the nature of God, but on a decree. This "middle knowledge" is allegedly different from free knowledge, however, in that it is not about things certainly future, or - to put it another way - it is not based on God's decrees but on the decrees of creatures.