The dictionary that followed

Dictionaries are often treated as courts of appeal, which is a misunderstanding of what the modern ones do.

A prescriptive dictionary states what is correct. A descriptive dictionary records what is used, in what proportions, by whom, and in which contexts. Most large English dictionaries have been descriptive for more than a century, which is why a word you dislike can appear in one without any editorial endorsement. The entry is a measurement, not a permission.

The method is corpus-based. Editors search a collection of hundreds of millions of words of real text and speech, count the senses in which a word actually occurs, and rank them by frequency. A sense that was first in 1950 may be fourth today, and the reordering is the dictionary's main form of argument. Nothing is added because it is logical or removed because it is regrettable.

This produces a predictable complaint. If a dictionary merely follows usage, it cannot tell a learner what to write in an examination. That is true, and it is why learner dictionaries exist as a separate genre, with explicit labels: informal, offensive, non-standard, mainly spoken. The labels are descriptive too, but they describe the social consequences of a choice rather than the choice itself, which is exactly what a learner needs.

The practical skill, then, is knowing which book you are holding. A historical dictionary tells you where a word has been. A corpus dictionary tells you where it is. A learner dictionary tells you what will happen if you use it in a formal letter. Only the third is advice, and it is the only one that was ever meant to be.