The "plain-language" movement responded to the incomprehensible business letter after correspondence became a fundamental business tool, but the cultural changes of the 1960s also propelled business and legal writing in a new direction. Plain writing is a movement for Concision and Clarity and, equally, informality. Writing advice often confuses the two plain-language agendas: communicative efficiency and social-power-distance reduction. Espousal of both purposes by one writing school helps explain their confusion, as does their relation to different senses of "formality." One sense is "strict adherence to established rules and procedures; rigidity"; another is "observance of form or ceremony.” (http://dictionary.reference.com/browse/formality) Formalities in the sense of ceremony impose rule-based rigidities, but not all rule-based rigidities come from formalities; much rigidity arises from wrong ideas about effective writing. The difference is important because the remedy for practices based on bad writing advice is elimination, for practices based on formality, moderation. Formalities also raise special problems of consistency; so getting the formality level consistently wrong can be better than occasional tonal inappropriateness.
Degrees of formality in writing express near-universal differences in personal address and related language use depending on conversers' social proximity and status. Friends may use forms of speech different from strangers, subordinates to social superiors different still. Where relationships with strangers and social unequals are fraught with hostility, forms serve to contain emotion by sacrificing communicative liberty. Modulating social distance through formality rigidifies language, but not all formulaic writing is rooted in formality. Native speakers grasp the distinction between social formality and pragmatic usage rule because a sense of social misstep or shame accompanies a true formality violation. To observers, our violation of the social formalities creates a perception of social impropriety, not merely communicative ineptitude. The first test is the introspection test. Do you say, "the court should order" or "plaintiff requests that the court order." Usually the first is better, but the second may be justifiable because its level of formality is higher. You can feel how the first nakedly asserts what in a less direct era requires a more indirect approach. You should adjust level of formality according to local custom; breaching the expected level of formality expresses egalitarianism, unwise courtroom politics more than inferior writing.
Since formalities are rules of respect, they apply to any medium, writing and speaking. The second test to distinguish formalities from errors, the speech test, is whether on formal occasions you speak as you write. You don't avoid contractions when speaking to strangers or superiors, showing that contraction avoidance isn't a formality. You should emphasize the test with the clearest results, and for contractions the speech test clarifies how much contraction avoidance rests on bad advice about effective practices rather than on formality. Negative modal verbs — such as "can't," "don't," "won't" — are contracted freely in speaking regardless of conversers' comparative social status. The introspection test confirms the speech test. Using these contractions doesn't offend a conversational partner, but contractions of participles fare differently. We don't use the contraction "would've" on formal occasions. We pronounce this contraction like "would of," and its enunciation involves a relaxed, slurring of consonants, showing minimal respect for status. Such manner of speaking is subtly insulting to those styled social superiors, even when their superiority is only procedural. More casual still is the negative of the past participle — for example, "wouldn't've." In legal writing, use the first class of contractions but not the formality-breaking second and third.