The LOB tag set, though larger and more delicate than that used for the Brown Corpus, represents a fairly broad classification. Greater delicacy had to be sacrificed in order to achieve the goal of tagging the entire LOB Corpus.

See further the list of tags in Appendix 4.

3.2 Differences with respect to the Brown tag set

The principal differences between the Brown and LOB tag sets are:

• the use of different tags for the definite (ATI) and the indefinite article (AT),
• the introduction of a special marker for one (CD1) and the use of 'suffixes' for inflected forms of the numerals;¹
• the non-use of the tag JJS for 'semantically superlative adjective' and the introduction of a special tag
• for attributive-only adjectives (JJB);
• the restriction of the tag NP to 'true' proper names and the use of special tags for other words habitually written with a word-initial capital (JNP, NNP, NPL,NPT);
• the introduction of new tags (NNU ) for abbreviated units of measurement., the use of different tags for first-, second-, and third-person pronouns (PP1... PP2, PP3 ... ) and also the use of A rather than S to mark the nominative form of pronouns (e.g. PP1A for I and PP1AS for we);
• the use of the tag RI for adverbs which are homographs of prepositions and a somewhat wider use of RP (adverbial particle);
• the introduction of special tags for some WH-words when used in a relative function (WDTR, WP$R, WPR, WPOR);
• the use of special tags for foreign words (&FW) and cited forms (NC). corresponding to hyphenated tags in the Brown Corpus;
• the introduction of the tags &FO (formula), CD-CD (hyphenated pair of cardinals), ZZ (letter), and XNOT (not is tagged * in the Brown Corpus);
• some differences in the tagging of punctuation marks;
• the introduction of ditto tags (see the next section).

In addition, contractions are split up in the LOB Corpus (see 5.3 and the end of 2.4), while the Brown Corpus uses compound tags. See Francis and Kucera (1979). These differences in the tag set and varying practice in some cases in applying the tags (especially a somewhat wider use of non-participle tags for -ed and -ing forms; cf 7.3 and 7.4) mean that comparisons between the tagged LOB Corpus and the tagged Brown Corpus must be made with caution.

Such idiom tagging makes it possible to avoid an arbitrary or counter-intuitive tagging at the level of the single word. See further 7.2.

The ditto tags occurring in the tagged corpus are included in the list in Appendix 4. The total number of words assigned such tags is fairly low (approx 5,500).