توضیح اینکه چیزی چطور کار می‌کندExplaining how something works

Process description: passive, sequence and purpose

توصیف فرایند در انگلیسی از سه ماده ساخته می‌شود و سرتاسر از حال ساده استفاده می‌کند — نه آینده، حتی برای فرایندی که قرار است رخ دهد. مجهول (درس ۴) تقریباً هر گام را حمل می‌کند، چون فاعل یا ناشناخته است یا بدیهی یا بی‌ربط: «the water is screened»، «the residue is removed»، «the sample is heated to 90°C». افزودن «by an operator» معمولاً سر و صداست. برای خودِ ماده وقتی خودبه‌خود عمل می‌کند معلوم را نگه دار: «the heavy particles settle»، «the mixture cools». توالی روی مجموعهٔ کوچکی از نشانگرها می‌چرخد و این‌ها جایگزین‌پذیر نیستند: first، then، next، after that، subsequently، finally برای ترتیب ساده؛ once، as soon as، when برای گامی که باید پیش از شروع گام بعد تمام شود («once the grit has settled…» — به حال کامل پس از once دقت کن)؛ while و as برای گام‌های هم‌زمان؛ at this point و by this stage برای جمع‌بندی وضعیت. بندِ هدف چیزی است که فهرست را به توضیح تبدیل می‌کند. so that + جمله، in order to + مصدر، to prevent + اسم یا ing: «the water is screened so that leaves are removed»، «chlorine is added to prevent bacteria from growing.» فرایندی که بدون بندهای هدف توصیف شود مثل دفترچهٔ راهنما خوانده می‌شود؛ آنکه دارد، مثل فهمیدن.

A process description in English is built from three ingredients, and it uses the present simple throughout — not the future, even for a process that will happen. THE PASSIVE (lesson 4) carries almost every step, because the agent is either unknown, obvious or irrelevant: "the water is screened", "the residue is removed", "the sample is heated to 90°C". Adding "by an operator" is usually noise. Keep the active for the substance itself when it acts on its own: "the heavy particles settle", "the mixture cools". THE SEQUENCE runs on a small set of markers, and they are not interchangeable: first, then, next, after that, subsequently, finally for plain order; once, as soon as, when for a step that must complete before the next begins ("once the grit has settled…" — note the present perfect after once); while and as for simultaneous steps; at this point and by this stage for taking stock. THE PURPOSE clause is what turns a list into an explanation. so that + clause, in order to + infinitive, to prevent + noun or -ing: "the water is screened so that leaves are removed", "chlorine is added to prevent bacteria from growing." A process described without purpose clauses reads like an instruction manual; one that has them reads like understanding.