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120 CHAPTER 5 The building blocks of natural language rule statements 5. a time of day on a day of the week: for example, "5 pm on Friday of each week" 31 ; 6. a time of day on a particular day in a week related to the current week or week under discussion: for example, "midday on Tuesday of the following week". 5.10 THE THREE USES OF `THAT' As we have now seen, `that' can be used in three distinct ways: 1. as a conjunction between a verb stating or questioning the truth of a proposition and that propo- sition, as in "the form specified that all passengers were adults" (in Section 5.3.5); 2. as a determiner, as in "I have the tickets for that flight" (in Section 5.4.2); 3. as a relative pronoun introducing a qualifying clause, as in "each bag that weighs more than 20 kg must be labeled with a `heavy bag' label" (in Section 5.8). 5.11 SUMMARY Natural language rule statements consist of words, each of which (each time it is used) belongs to a particular word class: noun, verb, etc. Some words belong to more than one class depending on their meaning and how they are used. Each noun is either a simple noun or a compound noun, which, as well as at least one simple noun, may include adjectives, prepositions, and (occasionally) numbers or conjunctions. Each proper name is the name of a single person, business (or other organization), place (continent, country, region, city, town, ocean, river, lake, mountain, building, etc.), time period (such as a day or month), musical or other artistic work, or brand or product name. Each verb is either a simple verb or a compound verb. A compound verb includes a simple verb, plus an adjective, noun, one or more prepositions, and/or an article. Verbs can take many forms: while fact types use only the third person singular present indicative forms (in both the active voice and the passive voice), rule statements may use the other forms. Determiners, adjectives, prepositions, conjunctions, and (occasionally) pronouns can be used in their own right (i.e., not as part of compound nouns or compound verbs) in rule statements; however, these words are never used in fact types except as parts of compound nouns or compound verbs. Not all English words of any class are available for use in rule statements in the constrained natural language proposed in this book. For example, a non-countable noun may not be used alone but only in a compound noun (as a pre-modifier of a countable noun) or in a compound verb. Also only a few determiners and pronouns, out of the many available in English, are used in this constrained natural language. Literals can also be used in rule statements: these express numeric or textual values, or time points, such as dates, times of day, or days of the week or month. 31 Known in Australia as "beer o'clock".