MMP.9:2 - Problem

A description can retain today’s quantity while losing what determines tomorrow’s. Differentiating a mean can introduce higher moments. Solving for an unobserved component can make its past influence explicit. Dropping a quickly decaying component can retain a lasting change it caused before decaying.

The missing contribution is often called an unclosed term: the proposed retained state does not determine it. A closure supplies a way to obtain or approximate that contribution from the information the reduced model carries. Its choice changes the resulting evolution.

Finding the unclosed term locates the difficulty. The remaining work is to derive a usable replacement and determine what that replacement permits the model to answer.