核心问题
…he often has to look for relationships in data. . . 据我所知,像 often 这样的频率副词,应当搁在实义动词之前、助动词或连系动词之后。在上面的句子里为什么频率副词搁在助动词 have to 之前呢?
词典解答
由于 have to 与一般的助动词在语法特点上并不完全相同,所以语法学家们把它划为半助动词。它与副词的相对位置,就是与一般助动词的区别之一。副词(often, frequently, usually, apparently 等)应当搁在 have to 之前。例如:
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We apparently have to go. 很显然我们必须去。
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People travelling long distances frequently have to decide whether they would prefer to go by land, sea, or air. (New Concept English, Book 3, L. 44) 人们作长途旅行时，往往不得不决定究竟取道陆路、海洋还是航空。
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In order to follow the buffalo, the Indians often have to move their camps. (DAI) 为了跟随野牛，印第安人常常不得不迁移营地。