Common words such as 'the' and 'and' are among the most difficult for lexicographers to define precisely, despite the fact that they are the words that cause least difficulty to native speakers. In practice, 'and' causes few problems to learners so, if I were you, I wouldn't bother too much about the more abstruse definitions such as these: 1) used to connect two identical words to indicate that things of the same name or class have different qualities: all human conduct is determined or caused—but there are causes and causes The definition is clear enough. Learners are unlikely ever to use this; they will probably say something like "all human conduct is determined or caused—but there different types of causes", and that's fine (2) archaic used to connect two numbers, implying succession: a line of men marching two and two Archaic - forget it.
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