There are many ways in which people address one another - the same propositional meaning may be conveyed in different forms:
Many languages have two or more versions of the pronoun meaning "you". "One of the pronouns is reserved for use with persons higher than the speaker in social status or persons with whom the speaker does not have a close personal relationship" (Romaine p156). These forms are conventionally referred to as "T" and "V" (as per French "tu"/"vous").
English used to have "thou/ye" but these have been lost now except, e.g. in some places in the North of England (especially with older people) and in certain religious settings. Other languages also experience change in the way that the two forms are used, which means that deciding which of the T/V alternatives to employ in any situation is not always straightforward, since an "incorrect" choice can give offence. For this reason, English is often preferred as a language of choice for international business.
Often the use of either T or V form may be used not just to signify intimacy or respect (respectively) with another person, but can be used to show solidarity, e.g. german students "don't say Sie (V form) to each other, they say du (T form)" - regardless of how well they are acquainted.
Trudgill's table (p92) shows how the usage of T/V forms might evolve, but it should be remembered that usage isn't ever static, and continues to evolve. Romaine (p157) discusses how the changes in usage in Sweden appear to correlate with changes in the political culture of that country.