Sixthly, for legal rules and procedures to command respect and support from administrators, there are at least three requirements. The substance of the rules must be compatible with the achievement of public objectives, and must be given effect predictably and in ways that take full account of the objectives of the public pro-grammar in which the administrators are engaged. It was suggested above that legal rules as applied in the courts usually have these characteristics. But in addition the rules themselves must be in a form which makes them appropriate to the taskof regulating decision making and action in thccontcxt of tlic iircti of public llt‘ll'l1ll1lSlFallOl1 in qiicslioii_ Rules hzive formal qualities whichiillicct thcir capacity to mlluciicc administrativeZlCllUl1_ As Dr Julia Black has CXl7léli|‘lE(.l,7 3 mlehas four dimensions: its content, llS immdatoi-ym, pcrinissive cliaractci', its lcgzil status and any Comscqiiciicc iittzicliing to non-compliance with itsand its striicture. The last three of thcse gl/Q 1-isieto its ‘mle-type‘. The last dimcnsioii, the sq-uc,turc ofthc rulc, itsclfhzis four aspects: its scopeor mclusivciicss; its precision or vagueness; thectisc with which it can be applied to concretesituutioiis (which Illack calls its ‘simplicity Q1’coinplcxity]; and its clarity or opacity, in termsof ‘the dcgrcc to which the rule contains words with well-dcfmcd and ll|ll’Cl'Sfllly 3.CCCp[@d mcanmgs"." Tlicrc arc both tactical and strategic reasons for using particulai rtilc-types, and the usc of plllllClll2ll‘ rulc-types has certain eonse.queiiccs, which arc independent olithe content ofthc rules, for the ability ofagencies to formulate and then achicvc policy objectives. A i1ile maylail througli being over- or under-inclusive. The search for precision may help to ensiirc consis- tcncy, hut only at the cost of increasing the sizeol‘ the rtilc-book, reducing the extent to which rules can be internalized, restricting potentiallyiiscftil discretion, and making it harder for offi- cials to implement policy flexibly. Clarity may make lift: easier for non-specialists, but create a barrier to the proper deploymem ofexpettise (for example, in the licld of medical assessrnents).'° if the form of rtilcs (legal or administrative)makes thcm diflicult for 2idrnini.strators to read, comprehend or apply in practice, they are likely to have little influence over day-to-day decision making and practice, although they may still exercise an influence over high-level policy making which scttlcs the general direction of2idmmisti'ativc effort.