Obviously, John and Mary stand respectively for the names of men and women known to the students.
Substitution—correlation drills lend themselves to practice of gender—number concords, as in the above example, to matching tenses of verbs with appropriate time expressions, to matching prepositions with the nouns, verbs or adjectives in a sentence, and so forth. Some important relationships, however, cannot be drilled in this way. For these relationships, transformation drills are needed.
Sample pair of sentences:
| Do you go swimming every day? | No, but I went swimming yesterday. |
Additional pairs of sentences:
| Do you buy cigarettes every day? | No, but I bought cigarettes yesterday. |
| Do you eat breakfast every day? | No, but I ate breakfast yesterday. |
| Do you get mail every day? | No, but I got mail yesterday. |
The purpose of this drill is of course to practice the single relationship which unites go with went, buy with bought, eat with ate and get with got.
A different kind of transformation drill combines two short sentences into a longer one:
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