有一读者问：有这样两个句子：
(1)People eat food off a fork, but never off a knife.
(2)Many more visitors than it can comfortably be poured in, off the regular steamers, off charted motorboats, and off yachts.
问这两句中的 off 如何解释？
介词 off=not on, away or down from 时，有时可与 from 互换，但 off 似乎较多用于口语，如：
(3)A book fell off the shelf.
(4)I bought it off a man I met in a public house. （有人认为off在此是俗语）
上述句（1）中的 off 亦可代之以 from，并可用于笔语中，再如：
(5)He ate it off the kitchen table.
(6)At night they would sit huddled round this stove, while they ate their supper off the laps.
(7)The master feeds me off his own plate. （摘自Aesop's Fables）
但当 off 用于离开或下马、下车、下船等时，则一般不可与 from 互换使用，上述句（2）即属于此种情况，再如：
(8)He got off his bicycle. （get off 已是一固定的短语动词）
(9)She jumped off the bus.
(10)He came off his horse when it refused to take a fence. （come off 也是一短语动词）
此外，还有不少情况习惯上皆用 off 而不用 from, 请读者随时留意，这里就不细说了。
