The rules work together. One rule alone does not make a text clear, but together they remove most sources of confusion. Use this overview to understand the purpose of each group, then study the details in the official ASD STE 100 PDF.
1. Words
The word rules are the base of STE. A writer uses approved words from the dictionary, or technical names and technical verbs that fit the rules. Each approved word has one part of speech and one meaning. For example, if a word is approved as a verb, you cannot also use it as a noun. If it is approved with one meaning, you cannot use it with a second meaning.
This idea is powerful. In normal English, a common word such as "run" or "check" can have dozens of meanings. A reader must guess the correct one from context. In STE, the reader does not need to guess.
Writers also keep the same word for the same thing. If you call a part a "bracket" in step 1, you do not call it a "support" in step 4. Technical names should be the names that the reader sees on the product or in the parts list.
2. Noun clusters
A noun cluster is a group of nouns in a row, such as "engine fuel pump inlet pressure sensor". Long clusters are hard to read, because the reader cannot easily see which word describes which. STE limits the length of noun clusters. When a cluster is too long, the writer breaks it up with prepositions ("the pressure sensor at the inlet of the fuel pump") or explains it once and then uses a shorter term.
3. Verbs
STE uses a small set of verb forms. Writers use the simple tenses (present, past and future), the imperative for instructions, and the past participle only in specific ways. Complex forms such as long continuous tenses or "would have been" structures are not used.
The active voice is the default. In an active sentence, the subject does the action: "The pump moves the fuel." In a passive sentence, the action happens to the subject: "The fuel is moved." The passive often hides who must act, which is dangerous in a procedure. STE permits the passive voice only in descriptive text, and only when it is really necessary.
Writers also avoid using -ing forms as verbs or adjectives in most cases, and avoid turning verbs into nouns. "Do an inspection of the valve" becomes "Examine the valve".
4. Sentences
Each sentence should give one topic. Sentences are short: the specification sets a maximum length for procedural sentences and a slightly longer maximum for descriptive sentences. Writers avoid omitting words such as "the" or "a" to make a sentence shorter, because this creates ambiguity. Lists and tables are useful when a sentence becomes too complex.
5. Procedures
Procedures tell the reader what to do. In STE, each instruction is a separate sentence, and each sentence is a command: the verb comes first. If two actions must happen at the same time, the writer may combine them. Conditions come first, so the reader knows the condition before the action: "If the light comes on, stop the engine."
Before
The cover can then be removed and the filter checked for contamination, replacing it if necessary.
STE version
1. Remove the cover. 2. Examine the filter for contamination. 3. If the filter is contaminated, replace it.
6. Descriptive writing
Descriptive text explains how something works or what it is. Here, STE permits slightly longer sentences, but the same principles apply. The writer starts with the most important information, uses paragraphs with one topic each, and keeps paragraphs short. Key words help the reader see how ideas connect, for example "because", "thus" or "but".
7. Warnings and cautions
Safety instructions must be impossible to misunderstand. A warning tells the reader about a risk of injury or death. A caution tells the reader about a risk of damage to equipment. STE asks the writer to start with a clear, simple command, and then to give the risk, so the reader knows what to do and why. Safety instructions must be specific, not general statements such as "be careful".
8. Punctuation and word counts
STE uses normal English punctuation, with a few clarifications. For example, writers use a colon to introduce a list, avoid semicolons in most cases and use hyphens to join words only where the specification permits. The specification also explains how to count words in a sentence, for example how to count numbers, units and identifiers.
How to practise these rules
Take a short procedure from your own work. Rewrite it one sentence at a time. First, put the verb first and use the active voice. Next, replace complex words with simple ones. Then, check sentence length. Finally, read it as a new user would. Our STE checker can flag many common issues, and the ASD STE 100 skill page has exercises with model answers.
Note: This page is an independent summary. It does not reproduce the text of the specification. For the exact rules and the dictionary, use the official document.