The following principles are seen to operate in the rules Pānini provides for Sanskrit grammar. (1) The obvious principle that the introduction of affixes and augments which condition sound replacements necessarily precede the latter. (2) Bracketing, whereby an operation whose condition is internal relative to a condition causing another operation applies prior to the latter. (3) The derivational prehistory of a form is pertinent to the operations which apply to it. (4) Blocking: a rule R2 is said to block an (...) R1 if, in a given domain, R1 tentatively applies (and would apply in the absence of R2) wherever R2 can apply, while R2 would be vacuous if R1 applied. (4a) Limited blocking, which obtains where R1 and R2 overlap but also have independent domains of application. These principles account for correct derivations in cases where post-Paninian grammarians invoked rule order: where two rules conflict, that one takes precedence which is stated later in the grammar. This principle is not generally tenable, since some derivations require that a rule stated previously in the grammar take precedence. Hence, the grammarians who invoke such rule ordering in cases of conflict must admit that only a knowledge of the correct results to be obtained by applying the rules allows one to correctly apply the rules in the first place. It is argued that Pānini avoided this weakness. (shrink)