by と with：交通手段・道具・方法

01by: methods and transport

Use by for transport and communication methods: by bus, by train, by plane, by email, by phone. No article follows — by the bus would mean next to that bus. Methods generalize the same way: pay by card, learn by reading, succeed by working hard. By answers the question how, at the level of the whole method.

02with: tools and company

Use with for the tool in your hand and the person beside you: cut with a knife, write with a pen, go with friends, live with family. The difference from by is concrete versus abstract — a knife is a physical object you hold, while by hand is the general method. Tests love this contrast.

03On foot, on the bus — and by Friday

Two famous exceptions live here. Feet take on, not by: go on foot. And once you board, you are on the bus or on the train — by describes the method of the whole trip, on describes where you ride. Then there is the deadline by: finish it by Friday means no later than Friday, while until Friday means keep working up to that point.

04The doer behind the action

In passive sentences, by names the doer: the book was written by her, the bridge was built by workers. If you can add the words created or performed before the noun, by is right. With never does this job — with a key opens the door, but only by her hands would name who did it.

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