 To begin, we assume that the human designer, after studying the world, uses the language of a particular logical system to give to our agent an initial set of beliefs \(\Delta_0\) about what this world is like. In doing so, the designer works with a formal model of this world, \(W\), and ensures that \(W\models\Delta_0\). Following tradition, we refer to \(\Delta_0\) as the agent’s (starting) knowledge base. (This terminology, given that we are talking about the agent’s beliefs, is known to be peculiar, but it persists.) Next, the agent ADJUSTS its knowlege base to produce a new one, \(\Delta_1\). We say that adjustment is carried out by way of an operation \(\mathcal{A}\); so \(\mathcal{A}[\Delta_0]=\Delta_1\). How does the adjustment process, \(\mathcal{A}\), work? There are many possibilities. Unfortunately, many believe that the simplest possibility (viz., \(\mathcal{A}[\Delta_i]\) equals the set of all formulas that can be deduced in some elementary manner from \(\Delta_i\)) exhausts all the possibilities. The reality is that adjustment, as indicated above, can come by way of any mode of reasoning – induction, abduction, and yes, various forms of deduction corresponding to the logical system in play. For present purposes, it’s not important that we carefully enumerate all the options. 