Knowledge (ʿilm) means that Allah already knows all that will occur. Will (mashīʾah) concerns what He wills to occur. Decree (qaḍāʾ) concerns His decision, and measure (qadar) concerns what is determined for each thing.
These four concepts are related but are not four interchangeable names for one meaning. Equating knowledge with will erases the difference between knowing and willing; reducing decree to mere knowledge loses its element of determination.
All things lie within Allah’s knowledge, will, decree, and measure, while the distinctions among these terms remain important.