Aristotle developed a system of logical inductive argument that we still use today. It takes the form: all birds are feathered, a robin is a bird, therefore a robin has feathers. The conclusion is dependent on the preceding two conditions being true. Such an argument can be applied to Parkinson’s. For example, Parkinson’s patients in the past gradually lost control of their body, Jonathan has Parkinson’s, therefore Jonathan will lose control of his body. This is the logical trap set by the prognosis of Parkinson’s.
Logical inductive arguments fall apart when they are applied to the future; they are undone by the unpredictability of future events. The first condition (e.g. all birds are feathered or Parkinson’s patients lose control) may not apply in the future. For the conclusion of an inductive argument to be valid at all times, the future has to be known. But a prognosis deals with a possible future based on what happened in the past. Therefore, the prognosis of Parkinson's is only a prediction and not a fact. No argument is future proof.