によって・
Reading one form through its surrounding relationship
によって does not carry one fixed English meaning. Look at the noun before it and ask what relationship that noun has with what follows: does it provide cases that vary, a method used intentionally, a cause producing a result, or the person or group responsible for a passive action? による packages the same relationships directly before a noun.
Ask what the marked noun is doing
The surrounding sentence—not the form alone—selects the meaning.
A factor with different cases
によって or によっては
The result differs by person, place, time, group, or case. Use the form with the added topic marker to single out some cases, often as exceptions.
The marked noun is not a tool or a cause; it supplies the cases being compared.
An intentional method
によって
A method, process, technology, investigation, or system is used to perform an action or achieve a goal.
For an ordinary handheld tool or another simple everyday means, the particle で is usually more natural.
A cause
によって
An event, condition, or force brings about a result without being deliberately used as a method.
This use is report-like and is heavier than common conversational ways of giving a personal reason.
The responsible doer
によって
A passive verb follows, and the marked person, creator, or institution performed or was responsible for the action.
Ordinary personal passive sentences generally mark the person with に instead.
A compact relationship before a noun
による
You want to place any of the four relationships directly before a noun.
This form does not resolve the meaning by itself. Read both nouns and mentally expand the phrase into a clause.
Variation means comparing cases
勤務先によって必要な書類が違います。
The required documents differ depending on the employer.
AnalyzeThe employers supply different cases, and the required documents vary across those cases.
Intentional method or resulting cause?
Automation is connected to a later result, but the intended relationship changes.
工程の自動化によって、生産時間を短縮した。
The production time was shortened through automation of the process.
AnalyzeAutomation is intentionally used to achieve the shorter production time.
急速な自動化によって、一部の仕事が失われた。
Some jobs were lost because of rapid automation.
AnalyzeAutomation brought about the loss; it was not used as a method for intentionally losing jobs.
Takeaway: If someone uses the noun to achieve the following action, read it as a method. If the noun simply brings about the following event, read it as a cause.
A passive verb can reveal the doer reading
この記念館は地元の建築家によって設計された。
This memorial hall was designed by a local architect.
AnalyzeThe architect performed the designing. This is formal attribution, not a cause or method.
The form changes with what follows
Use によって to connect a noun phrase to a clause. により is a more compact formal variant often seen in reports and notices. Before a following noun, use による. The special form によっては belongs to the variation use and selects certain cases.
Unpack the compact form
による can package all four relationships. Mentally turning the phrase back into a clause makes the intended reading easier to see.
部署による対応の違いを調べた。
We examined differences in responses among departments.
AnalyzeVariation: responses differ depending on the department.
新しい暗号化技術による情報保護が可能になった。
Information can now be protected using new encryption technology.
AnalyzeMeans: the technology is used to protect the information.
塩害による設備の故障が増えている。
Equipment failures caused by salt damage are increasing.
AnalyzeCause: salt damage brings about the failures.
市民団体による提案が議会で検討された。
A proposal made by a citizens' group was considered by the assembly.
AnalyzeResponsible doer: the citizens' group made the proposal.
More examples across the family
部門によって優先順位が異なります。
Priorities differ from department to department.
Analyze利用者によっては、この設定が不要です。
Some users do not need this setting.
Analyzeこの装置は画像認識によって欠陥を検出します。
This device detects defects through image recognition.
Analyze猛暑によって電力需要が急増した。
Electricity demand surged because of the extreme heat.
Analyze古い壁画は保存の専門家によって修復された。
The old mural was restored by conservation specialists.
Analyze地域による通信速度の差を測定した。
We measured regional differences in connection speed.
Analyze