A student can know what they want to say and still write like this:
The storm came. The wind was strong. The windows shook. The family was scared.
Nothing is grammatically broken. The problem is that the ideas remain side by side rather than being organised into relationships. Cause is not expressed. Emphasis is flat. Repetition is heavy. The reader has to do connective work that the writer has not yet learned to encode.
Traditional grammar lessons often respond by naming parts: adjective, conjunction, clause, adverbial, relative pronoun. That knowledge can be useful, but labels do not automatically become sentence control. A learner may correctly identify a subordinate clause on a worksheet and still produce a composition full of short repetitive sentences or long run-ons joined by “and.”
Sentence combining takes a different route. It gives students two or more basic sentences and asks them to make a stronger sentence while preserving meaning. The writer must decide what belongs together, what can be deleted, which relationship matters, where information should sit, and how punctuation changes with structure. Grammar becomes an act of composition.
The Australian Education Research Organisation describes sentence combining as an instructional technique for improving sentence quality, complexity and variety. Its practice guide notes more than 85 studies over roughly 50 years; most found improvements in sentence-level writing, while some also found gains in broader writing quality and revision. AERO also cautions that transfer from sentence-level improvement into whole-composition performance still needs further study and that some newer studies are small or concentrated in students with learning disabilities.
That makes sentence combining a good mechanism topic precisely because the claim can be bounded: it is not a complete writing curriculum. It is a structured way to make syntax usable.
The useful question is: how does combining simple ideas teach students to control sentence relationships rather than merely produce longer sentences?
The 50-second answer
Sentence combining works by making students solve a small writing problem repeatedly: several basic propositions need to become one effective sentence.
To solve it, the learner must decide:
- which information is central and which is supporting;
- whether ideas relate through addition, contrast, cause, time, condition, description or another relationship;
- what can be embedded or deleted without losing meaning;
- which conjunction, phrase or clause structure fits that relationship;
- where punctuation belongs;
- and whether the final sentence is clear, rhythmic and appropriate for the audience.
AERO recommends explicit modelling, guided practice, multiple acceptable solutions, discussion of why one combination may be more effective than another, and gradual fading from cued tasks to open tasks and eventually to students’ own writing.
The mechanism is controlled syntactic choice. Instead of asking students to “write more complex sentences,” teachers give them small decisions where complexity has a purpose.
The goal is not maximum sentence length. It is a writer who can choose among simple, compound and complex forms because each form changes meaning, emphasis and flow.
1. Combining begins with propositions, not grammar labels
A basic sentence usually expresses one proposition: something happened, someone did something, something has a property.
Sentence combining asks how several propositions relate before asking what grammatical form should carry them.
Concrete example.
- The river rose.
- Rain had fallen all night.
Possible combination: The river rose because rain had fallen all night.
The important decision is causal relationship. “Because” is useful because it encodes that relationship.
Boundary and caveat. Students still benefit from grammatical vocabulary, especially when discussing alternatives. But the label should serve the writing decision rather than become the entire lesson.
2. Longer is not automatically better
Weak sentence combining can produce monstrosities because students learn that the task is to fit everything into one sentence.
A strong combination preserves clarity while making relationships more precise.
Concrete example.
- The cyclist fell.
- The road was wet.
- She stood up.
- She checked her knee.
One sentence could contain everything, but two sentences may be stronger: Because the road was wet, the cyclist fell. She stood up and checked her knee.
Boundary and caveat. Sentence variety includes good short sentences. The technique should expand options, not create a bias toward complexity.
3. Coordination teaches equal relationships
Coordinating conjunctions can join ideas of relatively equal grammatical status.
And, but, so, or, yet are not interchangeable decorations. Each encodes a relationship.
Concrete example.
- Mira studied the map.
- She still took the wrong turn.
Mirа studied the map, but she still took the wrong turn.
The conjunction introduces contrast between preparation and outcome.
Boundary and caveat. Students who overuse “and” may need explicit contrast among coordination choices rather than simply being told to avoid the word.
4. Subordination teaches hierarchy
Subordinating conjunctions help writers decide which idea is the main assertion and which idea provides cause, condition, time, concession or another frame.
Concrete example.
- The experiment was repeated.
- The first result was unusual.
Because the first result was unusual, the experiment was repeated.
The sentence now tells the reader which event explains the other.
Boundary and caveat. Students can produce grammatically complex sentences with unclear logic. Relationship accuracy matters more than the presence of a subordinate conjunction.
5. Clause order changes emphasis
Because the first result was unusual, the experiment was repeated does not feel identical to The experiment was repeated because the first result was unusual.
Both are grammatical, but the opening frame changes what the reader encounters first.
Concrete example. Ask students to write both versions and explain which fits better after a paragraph discussing surprising data.
Boundary and caveat. Not every order difference creates a major meaning shift. The point is to make students notice information flow.
6. Embedding turns repeated information into structure
Basic sentences often repeat the same noun.
- The dog barked.
- The dog was nervous.
A combined version can embed the property: The nervous dog barked.
This reduces redundancy and makes description part of the noun phrase.
Boundary and caveat. Embedding every detail before a noun can overload the sentence. Writers need to decide which information deserves compression.
7. Relative clauses support precise identification
Two sentences can be combined by embedding one proposition as a relative clause.
- The scientist published the study.
- The scientist led the field team.
The scientist who led the field team published the study.
The clause identifies which scientist and preserves both propositions.
Boundary and caveat. Relative clauses can become ambiguous when pronoun reference is unclear. Students should check which noun the clause modifies.
8. Adverbials compress circumstance
Separate sentences about time, place, manner or reason can often become phrases.
- The team met.
- The meeting happened after lunch.
- They met in the library.
After lunch, the team met in the library.
Boundary and caveat. Compression should not hide information the reader needs to foreground. A circumstance may deserve its own sentence when it becomes important to the argument.
9. Participial phrases can connect simultaneous action
More advanced writers can compress actions into non-finite structures.
- Aisha opened the envelope.
- She held her breath.
Holding her breath, Aisha opened the envelope.
Boundary and caveat. Students need control of subject reference. Dangling modifiers appear when the implied subject of the phrase does not match the main clause.
10. Appositives can package definition
An appositive renames or explains a noun inside the sentence.
- The kakapo is a flightless parrot.
- The kakapo is endangered.
- It is native to New Zealand.
A possible combination: The kakapo, an endangered flightless parrot native to New Zealand, is protected through intensive conservation.
Boundary and caveat. Appositives are useful when the inserted information is genuinely supplementary. Too many interruptive phrases can damage flow.
11. Combining teaches deletion as well as addition
Students often think revision means adding more words. Combining requires removing repeated words and sometimes changing forms.
Concrete example.
- The engine was noisy.
- The noisy engine needed repair.
The repeated adjective should not survive twice. A stronger sentence may simply be: The noisy engine needed repair.
Boundary and caveat. Deletion is not automatically improvement. The writer must preserve every idea that still matters.
12. Word form can change during combination
AERO’s guide explicitly allows moving, adding, deleting or modifying words to create an effective combination.
That matters because natural English rarely emerges from joining two unchanged sentences with a connector.
Concrete example.
- The child smiled.
- The child was relieved.
The relieved child smiled or Relieved, the child smiled.
Boundary and caveat. Students need enough morphological knowledge to change word forms accurately. Sentence combining can expose those gaps.
13. Cued tasks reduce the first decision load
A beginning task may provide the intended conjunction or highlight repeated words.
- I will miss the bus.
- I leave late.
- Cue: if
I will miss the bus if I leave late.
The cue lets the learner practise the structure before selecting it independently.
Boundary and caveat. Cues should be temporary. If the teacher always supplies the connector, the student never learns relationship selection.
14. Open tasks shift responsibility to the writer
In an open task, students receive the propositions but no target word or structure.
Now they must decide what relation matters and which form expresses it.
Concrete example.
- Leonie finished the race.
- Her ankle hurt.
- She refused to stop.
Possible answers can foreground concession, sequence or determination.
Boundary and caveat. Open tasks are cognitively harder. Use them after students have a repertoire of structures to choose from.
15. More than one answer is a feature, not a problem
Sentence combining is powerful because several grammatical answers can preserve core meaning while changing emphasis or tone.
Concrete example.
- The museum was closing.
- We stayed to see the final room.
Possible combinations:
- Although the museum was closing, we stayed to see the final room.
- We stayed to see the final room even though the museum was closing.
Discussing the differences develops judgement.
Boundary and caveat. “More than one answer” does not mean every answer is equally effective or grammatically valid.
16. Comparison builds syntactic judgement
Students learn more when they compare combinations than when the teacher reveals a single model.
Ask which version is clearest, which is most concise, which fits a formal report, and which gives the strongest emphasis.
Concrete example. Put three student-generated versions on the board anonymously and evaluate them against meaning, clarity, rhythm and audience.
Boundary and caveat. Discussion should not become taste-only judgement. Require reasons tied to the writing purpose.
17. Meaning must survive the combination
A sentence can become grammatical while changing the original relationship.
- The alarm rang.
- The students left the room.
The students left the room because the alarm rang asserts cause. That may be correct—or it may add a relationship the source sentences did not establish.
Boundary and caveat. Combining is not permission to invent causation. Writers should distinguish implied relations from known ones.
18. Punctuation becomes functional
When sentence structure changes, punctuation changes with it.
This gives punctuation a reason. A comma after an introductory subordinate clause, punctuation around a non-essential appositive, or a comma before certain coordinated independent clauses can be taught inside meaning-making.
Concrete example. Compare When the bell rang the class moved with When the bell rang, the class moved and explain what the comma signals.
Boundary and caveat. Punctuation conventions vary by structure and style. Avoid giving one-rule slogans that later fail.
19. Sentence boundaries become easier to diagnose
Students who produce fragments or run-ons often benefit from learning how complete propositions can be combined legitimately.
A fragment such as Because the experiment failed becomes visibly incomplete unless another clause completes the relationship.
Concrete example. Pair fragments with possible main clauses, then ask students to create complete combinations.
Boundary and caveat. Sentence combining is one tool for boundary control. Some students need direct instruction in clause completeness as well.
20. Oral rehearsal can lower transcription load
AERO lists oral rehearsal as one way to increase scaffolding.
Saying two or three possible combinations aloud lets students hear rhythm and check logic before writing.
Concrete example. Partners generate one because version and one although version before choosing one to write.
Boundary and caveat. Oral fluency can mask punctuation or spelling needs. Spoken rehearsal should lead back to written construction.
21. Student writing is a high-value source of material
Generic exercises build technique. Sentences from the student’s own draft create a bridge to authentic revision.
Concrete example.
Original: The cave was dark. The cave was cold. We went deeper. We were nervous.
The student experiments with combinations while keeping the narrative purpose in view.
Boundary and caveat. Do not make every early draft a grammar repair exercise. Writers need protected time to generate ideas before sentence-level editing.
22. Mentor texts can supply authentic structures
Published sentences can be deconstructed into basic propositions and then rebuilt.
This shows students that syntax is a choice made by real writers, not merely a school exercise.
Concrete example. Take a concise sentence from an informational text, split its embedded details into separate propositions, then ask students to recombine before seeing the original again.
Boundary and caveat. Use short excerpts and respect copyright. The learning goal is structural analysis, not imitation of a living author’s distinctive style.
23. Discipline matters
Science, History, Mathematics and English use sentence relationships differently.
Science may need cause, condition and comparison. History may need time, concession and evidence. Mathematics explanations may need condition and logical consequence.
Concrete example. Combine:
- The variable increases.
- The slope is positive.
Different combinations reveal whether the relation is definitional, causal or conditional.
Boundary and caveat. Do not force literary complexity into technical writing where clarity and precision require simpler structure.
24. Academic language often requires compression
School writing asks students to package ideas more densely than everyday speech.
Sentence combining can help students shift from conversational chains—“and then… and then…”—toward explicit relationships.
Concrete example.
Spoken-like: The government changed the rule and people reacted and there were protests.
More controlled: After the government changed the rule, public opposition intensified and protests followed.
Boundary and caveat. Formal does not mean inflated. Students should avoid replacing clear verbs with unnecessary nominalisations or jargon.
25. Variety should serve discourse, not a quota
A student may be told to include one simple, one compound and one complex sentence. That can produce artificial writing.
A better goal is matching sentence structure to rhetorical function.
Concrete example. Use a short sentence for emphasis after a long explanatory sequence: The bridge failed.
Boundary and caveat. Sentence variety is an outcome of control, not a checklist of forms.
26. Rhythm is part of readability
AERO includes rhythm among criteria for evaluating combinations.
Students can hear whether repeated clauses become monotonous or whether a long sentence needs relief.
Concrete example. Read two versions aloud: one with repeated “and,” another with a subordinate clause and a shorter closing sentence.
Boundary and caveat. Rhythm is partly stylistic and context-dependent. It should not overrule clarity.
27. Audience changes the best combination
A sentence for a young reader may need different density from a sentence in a scientific report.
Concrete example. Combine the same facts once for a Primary 4 explanation and once for a formal school report.
Boundary and caveat. Do not treat complex syntax as inherently more mature. Appropriate syntax depends on audience and purpose.
28. Sentence combining can support revision, not just first construction
Once students have practised controlled tasks, they can search their own draft for repeated simple sentences, overloaded coordination or unclear relationships.
Concrete example. Highlight one paragraph and ask: Which two sentences belong together? Which long sentence should actually be separated?
Boundary and caveat. Revision also involves ideas, organisation and evidence. Sentence combining should not narrow revision to grammar.
29. Students need a repertoire before independent choice
Open choice is only useful when the learner has alternatives available.
Teachers should deliberately build structures: coordination, subordination, relative clauses, phrase embedding, apposition and other age-appropriate options.
Concrete example. Keep a class “relationship bank” organised by meaning—cause, contrast, time, condition—not only by conjunction lists.
Boundary and caveat. A bank should support retrieval, then fade. Permanent dependence on a connector sheet limits independent control.
30. Feedback should target effectiveness, not only correctness
A grammatically correct sentence can still be vague, repetitive or badly suited to the paragraph.
AERO recommends considering clarity, rhythm and audience suitability.
Concrete example. Instead of “correct,” feedback says: “This is grammatical, but putting the cause first makes the reader understand the decision sooner.”
Boundary and caveat. Correctness still matters. Effectiveness is an additional layer, not a substitute for syntax accuracy.
31. Practice should be sustained enough for transfer
One lesson on conjunctions rarely changes spontaneous writing.
Students need repeated combining, discussion and revision across different topics until the choice process becomes available during real composition.
Concrete example. Spend brief periods across several weeks combining sentences drawn from current curriculum content rather than one isolated grammar unit.
Boundary and caveat. The research base is stronger for sentence-level improvement than for guaranteed whole-composition transfer. Teachers should check actual drafts.
32. The end state is choice, not visible use of the technique
A writer who has learned sentence combining should not need to consciously merge teacher-supplied kernel sentences forever.
The practice succeeds when the learner generates ideas in relationships from the start and can revise when the relationship is unclear.
Concrete example. A student independently changes two choppy sentences into one causal sentence during editing, then deliberately leaves the next sentence short for emphasis.
Boundary and caveat. Mature writing still includes revision. Automaticity means greater control, not the disappearance of decision-making.
Worked cases
Case 1 — The “and” chain
Ben writes:
The volcano erupted and the ash rose and people left and flights stopped and it was dangerous.
The teacher first separates the propositions. Ben identifies cause, sequence and result. He produces:
When the volcano erupted, ash rose into the atmosphere. Because visibility became dangerous, flights stopped and nearby communities evacuated.
The improvement does not come from banning “and.” It comes from naming different relationships.
Case 2 — The sentence that became too clever
Mira combines four facts into a 47-word sentence with two relative clauses, three commas and a participial phrase. It is grammatical but difficult to read.
The class tests where the reader loses the main action. Mira splits the sentence into two, keeping one embedded clause.
The lesson is that syntactic control includes stopping the combination.
Case 3 — From cue to open choice
Aisha initially combines sentences only when the teacher supplies because, although or when. After guided practice, the cues are replaced by relationship categories: cause, contrast, time.
Later, she receives two propositions with no cue and chooses although because the second fact conflicts with the expectation created by the first.
The learning has moved from filling a connector slot to selecting a relationship.
Case 4 — Revision inside Science
Ryan writes:
The water heated. The particles moved faster. The temperature increased.
During sentence-combining review, he creates:
As the water was heated, its particles moved faster and the temperature increased.
The Science teacher then asks whether the sentence accurately represents the causal mechanism. Syntax and subject knowledge are checked together.
Practical route for teachers
Choose a narrow relationship or structure and model several worked examples. Narrate the decision: what repeats, what can be deleted, which idea should lead, what the connector means, and how punctuation changes.
Begin with cued tasks if students need them. Move to category cues, then open tasks. Invite more than one answer and compare versions using meaning, clarity, rhythm and audience.
Keep practice brief but sustained. Draw sentences from current reading, curriculum content and, later, students’ drafts.
Do not reward length. Praise justified choice.
A useful sequence is:
- identify propositions;
- name the relationship;
- generate two possible combinations;
- choose the more effective version for the purpose;
- punctuate it;
- explain why it works;
- transfer the decision into authentic writing.
Practical route for learners
When your writing feels choppy, do not randomly add conjunctions.
Ask:
- Which sentences are about the same event or idea?
- What is the relationship: addition, contrast, cause, time, condition, description?
- Which idea is most important?
- What information repeats?
- Can one idea become a phrase or clause inside another?
- Would combining make the sentence clearer—or too crowded?
Try two versions. Read them aloud. Choose based on meaning and flow.
When a sentence becomes hard to understand, split it. Control means being able to combine and separate.
Practical route for parents and families
Parents do not need to teach formal grammar terminology to support sentence control.
Take two short factual sentences and ask, “Can we make one sentence without losing either idea?” Then ask, “Is there another way?”
For example:
The dog hid. The thunder was loud.
Possible versions:
- The dog hid because the thunder was loud.
- Because the thunder was loud, the dog hid.
- Frightened by the loud thunder, the dog hid.
Discuss what changes.
Keep the activity short and playful. The purpose is flexible expression, not correcting every sentence the child speaks.
Common failure modes
- Treating longer sentences as automatically better.
- Giving students conjunction lists without teaching relationships.
- Accepting any grammatical combination without checking meaning.
- Keeping cue words forever.
- Teaching only one “correct” answer when several are defensible.
- Combining so much information that the main clause disappears.
- Using grammar labels with no revision or composition task.
- Correcting punctuation without explaining the structure that requires it.
- Practising isolated exercises but never using students’ own writing.
- Using sentence combining as the entire writing curriculum.
- Assuming sentence-level gains automatically guarantee better whole compositions.
- Forcing complex sentences into technical writing where a short sentence is clearer.
- Rewarding variety as a checklist rather than rhetorical control.
Frequently asked questions
Is sentence combining just grammar instruction?
It teaches grammar through sentence construction and revision. Students may learn grammatical terms, but the primary activity is making meaning-bearing choices.
Is there one correct combination?
Often no. Several versions can be grammatical and accurate. The useful discussion is which version best fits clarity, emphasis, rhythm and audience.
Should students always create complex sentences?
No. Good writing needs controlled variety, including simple sentences. The goal is choice.
Does sentence combining improve overall writing?
Research strongly supports sentence-level benefits, and some studies report broader writing and revision gains. AERO also notes that more research is needed on transfer into compositional writing, especially across broader populations.
When should cues be removed?
As soon as students can use the structure reliably enough to choose among options. Move from supplied words to category cues to open tasks.
Can sentence combining be used outside English?
Yes. It can use History, Science, Geography or other curriculum content, provided the final sentence remains accurate to the discipline.
What should feedback focus on?
Correctness, preserved meaning, clarity, rhythm, emphasis and suitability for audience and purpose.
A four-phase teaching sequence
A sustainable sentence-combining sequence can move through four phases.
Phase one: notice and model. The teacher shows how two propositions can be combined and narrates why the relationship matters.
Phase two: cued control. Students use supplied conjunctions, highlighted repeated words or sentence frames. The decision space is small enough for them to focus on one structure.
Phase three: open choice. Cues disappear. Students produce several solutions and justify which best serves the meaning.
Phase four: authentic revision. Students locate opportunities inside their own writing, including places where a long sentence should be split.
The sequence prevents two common failures: leaving students in fill-the-gap grammar forever, or asking them to “vary their sentences” without enough repertoire to do so.
Students can move backward temporarily when a new structure is introduced. Scaffolding is not a grade level; it is support matched to the current decision.
A relationship-first classroom language
Teachers can organise sentence work around meanings rather than terminology alone.
Ask, “Are these ideas happening at the same time or one after the other?” “Does one cause the other?” “Is the second idea surprising given the first?” “Is one idea a condition?” “Does this information identify the noun or simply add detail?”
That language helps students choose structures because they understand the relation to encode.
Formal terms can then sharpen discussion: coordinating conjunction, subordinate clause, relative clause, appositive, adverbial.
The order matters. If the first question is “Which subordinating conjunction should we use?”, a student may select from a list without understanding why. If the first question is “What relationship do these ideas have?”, grammar becomes a tool for the answer.
A progression from speech-like to academic syntax
Many developing writers produce text that mirrors conversational sequencing: and then, repeated subjects, short clauses, vague pronouns and ideas added in the order they occur.
Sentence combining can help them compress when written language requires density.
Start with familiar relationships: time and cause. Move into contrast, condition, concession, embedded definition and precise modification. In informational writing, students can learn to package background information inside noun phrases or relative clauses. In argument, they can use concession to acknowledge an opposing condition before stating a claim.
The goal is not to make writing sound artificially formal. It is to give the student more ways to organise information when speech-like chaining is insufficient.
Academic language is partly a problem of syntax: how much relationship the sentence can make explicit without losing readability.
Using sentence combining to teach revision
Revision often feels mysterious to students because they are told to “improve the sentence” with no operation in mind.
Sentence combining gives a concrete revision repertoire:
- merge repeated propositions;
- make cause explicit;
- foreground a condition;
- embed non-central information;
- reduce repeated nouns;
- change clause order;
- split overloaded sentences.
Teachers can mark a paragraph with symbols indicating possible operations rather than rewriting it for the student.
For example, two adjacent sentences might receive “C?” for possible combination. A long sentence might receive “S?” for possible split. The student must decide, not obey automatically.
This makes revision a sequence of controlled choices rather than cosmetic editing after the “real” writing is finished.
How to evaluate transfer into real writing
A student can become excellent at worksheet combinations while their compositions remain unchanged. Transfer therefore needs direct checking.
Collect short authentic writing before a teaching sequence and again several weeks later. Look at sentence boundaries, repetitive coordination, range of relationships, clarity of reference and whether complex structures remain accurate.
Do not reward complexity alone. A draft with more subordinate clauses but more errors is not automatically better.
Also inspect revision behaviour. Does the learner independently combine repetitive sentences? Can they explain why a sentence was split? Do they select structures appropriate to the genre?
AERO’s evidence caveat is important here: sentence-level improvement is the clearest claim. Schools should verify whether their teaching sequence is reaching paragraph and composition quality rather than assuming it.
Sentence combining for multilingual learners
Multilingual learners may have rich ideas while still developing the syntax expected in the language of instruction.
Sentence combining can help because the propositions are supplied, reducing idea-generation load while attention shifts to relationships and sentence form.
Oral rehearsal is especially useful. Students can say several combinations, compare how conjunctions change meaning, then write.
Teachers should avoid treating home-language influence as deficient thinking. The task is to expand control of written English structures while recognising that other languages may package information differently.
Where appropriate, comparing how a relationship such as cause or condition is expressed across languages can strengthen metalinguistic awareness.
The final goal is added repertoire, not replacing one legitimate language system with a judgement about intelligence.
One final rule: complexity must earn its place
Every added clause creates a cost for the reader. The sentence must repay that cost by making a relationship clearer, compressing useful information or controlling emphasis.
If the combined sentence merely sounds “more advanced,” it has missed the purpose.
A mature writer can choose:
The lights failed. Everyone stopped.
Or:
When the lights failed, everyone stopped.
Or:
Everyone stopped when the lights failed.
The best version depends on what the paragraph needs the reader to notice.
That is the real achievement of sentence combining: not producing complicated sentences, but making syntax available as a deliberate instrument.
Sources and further reading
- Australian Education Research Organisation — Sentence combining
- AERO — Sentence combining practice guide PDF
- What Works Clearinghouse — Teaching Elementary School Students to Be Effective Writers
Continue exploring on eduKateSG
- How X Works Hub
- What Is Syntax?
- How English Works | Sentence-Relative Clauses
- Why Do Strong Readers Know More Than the Words on the Page?
The final idea
Sentence combining is a small exercise with a large intellectual demand.
The learner must decide what belongs together, what relationship holds, what can disappear, what should be foregrounded and how grammar can carry those decisions without losing clarity.
That is why the technique can do more than make sentences longer. Used explicitly, repeatedly and then transferred into revision, it turns grammar into choice.
The governing principle is: combine ideas to make their relationship clearer, not to make the sentence look more advanced. When the relationship is already clear, stop.