If sense is to be identified with algorithm, perhaps the most basic question is: what is an algorithm. For Moschovakis, as for many working mathematicians, an algorithm is an abstract mathematical object, in the same way that a number is. Of course one uses special notation to work with a number or an algorithm, but notation is syntactic while mathematical objects are semantic (even ideal). Algorithmic subject matter may vary: an algorithm for baking a cake does not operate in the same space as an algorithm for solving quadratic equations. Some formalism is needed so that algorithms can be specified, and this machinery should be suitable for all subjects, yet as simple as possible. There are several general, but equivalent, approaches to algorithmic specification across a range of subject matters. Moschovakis (1994) introduces a very simple, direct mechanism which he calls the Lower Predicate Calculus with Reflection, where reflection essentially means self-reference. Of course not all algorithms terminate, and consequently the underlying truth value space needs some consideration, but a solution along Kripke’s lines in his Theory of Truth works well. We lead up to a general definition via some (for the time being) informal examples.