Use by for agents, methods, deadlines, measurements, proximity, and gradual change. This lesson focuses on the choices that most often affect meaning, accuracy, and natural English.
Core idea
Grammar is easier to use when you connect the form to the message it carries. Read the complete sentence, identify the relationship between its parts, and then choose the structure that expresses that relationship clearly.
Forms and choices
- In a passive clause, by introduces the agent.
- For methods, use by + -ing or common transport phrases such as by train.
- For deadlines, by means no later than.
- Use by for differences, dimensions, rates, and nearby position.
Original examples
- The mural was painted by local artists.
- We reduced waste by reusing the containers.
- The table measures two meters by one meter.
- There is a small bench by the fountain.
Notice that each example gives enough context to make the grammar choice meaningful. When you write your own example, include a real person, time, place, purpose, or result instead of practicing an isolated fragment.
A reliable decision process
- Find the main verb and its subject.
- Decide what relationship you need to express: time, quantity, comparison, purpose, position, or attitude.
- Check the words immediately before and after the gap.
- Read the full sentence again and confirm both meaning and form.
Common mistakes to avoid
- Do not choose a form only because it resembles a structure in another language.
- Do not ignore whether the next element is a noun phrase, a clause, a base verb, or an -ing form.
- Do not memorize an example without understanding why that form fits its context.
Test and writing strategy
In a gap-fill question, use the surrounding grammar before judging vocabulary. In your own writing, prefer the shortest structure that preserves your exact meaning. During revision, search for the target words from this lesson and inspect each one in its full clause.