Sentence Structure and Clauses

Lesson 9: Common Errors with Clauses and Sentence Structure

Lesson: 9 of 9 | Level: 🟠 Intermediate — 🟣 Upper-Intermediate

1. Lesson Overview

Every lesson in this module has built a systematic and comprehensive understanding of English sentence structure — from the foundational distinction between phrases and clauses, through the full range of subordinate clause types, to the advanced techniques of clause reduction and sentence combining. This final lesson draws all of that knowledge together by cataloguing and correcting the most common, most persistent, and most significant errors that learners make in the construction and use of clauses and sentences — organised into clear categories, with the grammatical and communicative principles that underlie each correction explained in full.

This lesson is designed to serve both as a diagnostic reference — allowing learners and teachers to identify the specific areas of sentence structure where accuracy needs attention — and as a final consolidation of the module’s content.

Objectives

By the end of this lesson, you will be able to:

• Identify all the major categories of error in clause and sentence structure
• Understand the grammatical and communicative principles underlying each correction
• Apply accurate sentence structure across all clause types and combining strategies
• Avoid the most persistent errors in both production and analysis

2. Core Content

A. Sentence Boundary Errors

Sentence boundary errors involve misidentifying where one sentence ends and another begins — either by creating incomplete sentences (fragments), joining sentences incorrectly (comma splices), or running them together without punctuation (run-ons).

Error type 1 — Sentence fragments

A sentence fragment is a group of words presented as a complete sentence but lacking a main clause — either because it has no finite verb, no subject, or because it is a subordinate clause without a main clause to attach to.

For example:

Although the conditions were difficult. ❌ (subordinate clause without a main clause) The team working at extreme depths. ❌ (noun phrase + participial phrase — no finite verb) Because baseline measurements had not been established. ❌ (subordinate clause) For example, the discovery of hydrothermal vents in 1977. ❌ (noun phrase — no finite verb)

Corrections

Although the conditions were difficult, the team completed the survey. ✅ The team working at extreme depths faces enormous technical challenges. ✅ Because baseline measurements had not been established, the impact could not be assessed. ✅ For example, the discovery of hydrothermal vents in 1977 transformed our understanding of life. ✅

Error type 2 — Comma splices

A comma splice occurs when two main clauses are joined by a comma alone — without a coordinating conjunction or a semicolon.

For example:

The sample size was small, the findings were significant. ❌ Scientists have studied vents for decades, much remains unknown. ❌ The equipment failed, the team returned to port. ❌

Corrections

Four standard corrections for each comma splice:

1. Separate with a full stop: The sample size was small. The findings were significant.
2. Use a coordinating conjunction: The sample size was small, but the findings were significant.
3. Use a semicolon: The sample size was small; the findings were significant.
4. Use subordination: Although the sample size was small, the findings were significant.

Error type 3 — Run-on sentences

A run-on sentence joins two main clauses with no punctuation or conjunction at all.

For example:

The team collected samples the data was sent for analysis. ❌ Scientists have studied the deep ocean for decades they have found many new species. ❌

Corrections

Apply the same four corrections as for comma splices — separate, coordinate, punctuate with semicolon, or subordinate.

B. Errors with Coordinating Conjunctions

Error type 4 — Using but after although

Although and but both express contrast. Using both in the same sentence is redundant.

Although the sample size was small, but the findings were significant. ❌ Although the sample size was small, the findings were significant. ✅

Error type 5 — Treating however as a coordinating conjunction

However is a conjunctive adverb — not a coordinating conjunction. It cannot join two main clauses with only a comma.

The sample size was small, however the findings were significant. ❌ (comma splice) The sample size was small; however, the findings were significant. ✅ The sample size was small. However, the findings were significant. ✅

Error type 6 — Non-parallel coordination

When coordinating two or more elements, they must be grammatically parallel — matching forms for matching logical functions.

The team collected samples, analysed the data, and the findings were published. ❌ (non-parallel — shift from verb to passive clause) The team collected samples, analysed the data, and published the findings. ✅

The methodology was rigorous, comprehensive, and drew on the best technology. ❌ The methodology was rigorous, comprehensive, and technologically sophisticated. ✅

C. Errors with Subordinating Conjunctions

Error type 7 — Using although with but

As noted above — although and but express the same contrast relationship. Using both simultaneously is redundant and grammatically incorrect.

Although the conditions were difficult, but the team completed the survey. ❌ Although the conditions were difficult, the team completed the survey. ✅

Error type 8 — Using despite with a finite clause directly

Despite and in spite of are prepositions — they cannot be followed directly by a finite clause.

Despite the conditions were difficult, the team completed the survey. ❌ Despite the difficult conditions, the team completed the survey. ✅ (preposition + noun phrase) Despite the fact that the conditions were difficult, the team completed the survey. ✅ (the fact that + clause)

Error type 9 — Using will in time clauses

Will is not used in time clauses introduced by when, while, before, after, until, as soon as, once, and by the time. The simple present or present perfect replaces the future in these clauses.

When the expedition will return, the analysis will begin. ❌ When the expedition returns, the analysis will begin. ✅

As soon as the team will have completed the survey, it will return. ❌ As soon as the team has completed the survey, it will return. ✅

Error type 10 — Unless with a negative clause

Unless means if not — adding not to the clause it introduces creates a double negative.

The expedition will not proceed unless the safety requirements are not met. ❌ The expedition will not proceed unless the safety requirements are met. ✅

Error type 11 — Using since ambiguously

Since can express either time (from a past point to the present) or cause (because). Using it in contexts where the meaning is ambiguous weakens the sentence.

Since the team began the survey, the results have been surprising. (time — clear) Since the results were surprising, the team decided to repeat the analysis. (cause — clear) Since the equipment was installed, it has been producing anomalous readings. (time or cause? — potentially ambiguous)

When ambiguity is possible, use because for cause and ever since for time.

D. Errors with Relative Clauses

Error type 12 — Using that in non-defining relative clauses

That cannot be used in non-defining relative clauses — which, who, and whom only.

The vent community, that was discovered in 1977, is still studied. ❌ The vent community, which was discovered in 1977, is still studied. ✅

Error type 13 — Using which for people

Which refers to things and animals — not to people. Use who or whom for people.

The scientist which made the discovery retired last year. ❌ The scientist who made the discovery retired last year. ✅

Error type 14 — Double subject in relative clauses

When the relative pronoun is the subject of the relative clause, no additional subject pronoun is needed.

The species that it was discovered in 1977 is unique. ❌ (double subject — that and it) The species that was discovered in 1977 is unique. ✅

Scientists who they study the ocean face challenges. ❌ Scientists who study the ocean face challenges. ✅

Error type 15 — Double object in relative clauses

When the relative pronoun is the object of the relative clause, no additional object pronoun is needed.

The data that the team collected it was remarkable. ❌ The data that the team collected was remarkable. ✅

The researcher whom the committee honoured him retired. ❌ The researcher whom the committee honoured retired. ✅

Error type 16 — Using that after a preposition

That cannot be used after a preposition in relative clauses — use which or whom.

The site at that the vents were discovered is now protected. ❌ The site at which the vents were discovered is now protected. ✅

Error type 17 — Missing comma in non-defining relative clauses

Non-defining relative clauses must be enclosed in commas — the clause is supplementary and the commas signal this.

The vent community which was discovered in 1977 is still studied. ❌ (missing commas — reads as defining) The vent community, which was discovered in 1977, is still studied. ✅

Error type 18 — Interrogative word order in relative clauses

Relative clauses always use declarative word order — not interrogative inversion.

The reason why did the species disappear is unknown. ❌ The reason why the species disappeared is unknown. ✅

The site where was the vent discovered is now protected. ❌ The site where the vent was discovered is now protected. ✅

E. Errors with Noun Clauses

Error type 19 — Omitting that in formal writing

In formal and academic writing, that should be retained after reporting verbs and in noun clause constructions — omitting it produces an informal effect.

Scientists confirmed the new species was from an undescribed genus. ❌ (formal — that required) Scientists confirmed that the new species was from an undescribed genus. ✅

Error type 20 — Using if instead of whether in formal noun clauses

Whether is required — not if — when the noun clause is the subject of the sentence, follows a preposition, or appears after be as a complement.

If the methodology is robust depends on the sample size. ❌ Whether the methodology is robust depends on the sample size. ✅

The debate about if deep-sea mining is sustainable continues. ❌ The debate about whether deep-sea mining is sustainable continues. ✅

Error type 21 — Wrong verb form in subjunctive that-clauses

After verbs and adjectives expressing recommendation, requirement, and necessity, the bare subjunctive or should + bare infinitive is required — not the indicative form.

It is essential that all instruments are calibrated. ❌ (indicative — non-standard in formal British English) It is essential that all instruments be calibrated. ✅ (bare subjunctive) It is essential that all instruments should be calibrated. ✅ (should + bare infinitive — British English alternative)

The committee recommended that the survey was extended. ❌ The committee recommended that the survey be extended. ✅

Error type 22 — Interrogative word order in noun clauses

Noun clauses always use declarative word order — not the inverted word order of direct questions.

Scientists do not know what does the data show. ❌ Scientists do not know what the data shows. ✅

The committee asked where was the vent field located. ❌ The committee asked where the vent field was located. ✅

F. Errors with Non-Finite Clauses

Error type 23 — Dangling participles

The most common error in non-finite clause use — the implied subject of the participial clause must be the subject of the main clause.

Studying the data, the anomaly was immediately apparent. ❌ (the anomaly cannot study data) Studying the data, the researchers immediately noticed the anomaly. ✅

Having secured the funding, the expedition was planned. ❌ (the expedition cannot secure funding) Having secured the funding, the team began planning the expedition. ✅

Error type 24 — Wrong participle form — active vs. passive

The distinction between present and past participial clauses must reflect whether the relationship is active or passive.

The data collecting over eighteen months has been analysed. ❌ (the data does not collect — passive relationship) The data collected over eighteen months has been analysed. ✅

Organisms studied in vent ecosystems have evolved unique adaptations. ❌ (the organisms actively live there — active relationship) Organisms living in vent ecosystems have evolved unique adaptations. ✅

Error type 25 — Using infinitive after first/last/only without to

After first, last, only, next, and superlatives, the to-infinitive is required — not the bare infinitive or participial form.

Darwin was the first scientist discovering the mechanism of natural selection. ❌ Darwin was the first scientist to propose a fully developed mechanism for natural selection. ✅

It was the most significant finding ever making in deep-sea biology. ❌ It was the most significant finding ever made in deep-sea biology. ✅

Error type 26 — To-infinitive after purpose conjunctions

After in order to and so as to, the bare infinitive is used — not to again.

The team moved slowly in order to to avoid disturbing the organisms. ❌ The team moved slowly in order to avoid disturbing the organisms. ✅

G. Errors with Sentence Combining

Error type 27 — Over-coordination — excessive use of and

Chaining multiple clauses with and produces a monotonous and immature style — subordination and embedding are almost always more effective.

The team collected samples and they analysed the data and they published the findings and they presented them at the conference. ❌ The team collected samples, analysed the data, published the findings, and presented them at the international conference. ✅

Error type 28 — Over-embedding — sentences too complex to parse

Embedding too many clauses within a single sentence makes it difficult to read.

Scientists who study vent ecosystems that have been damaged by warming, acidification, and mining operations, which began expanding rapidly in the early 21st century, face enormous challenges. ❌ (three levels of embedding — difficult) Scientists studying ecosystems damaged by warming, acidification, and early 21st-century mining face enormous challenges. ✅ (reduced — clearer)

Error type 29 — Mixed structures in parallel lists

When listing parallel ideas, all elements must be grammatically parallel.

The survey produced valuable data, confirmed existing models, and several new species were identified. ❌ The survey produced valuable data, confirmed existing models, and identified several new species. ✅

3. Usage in Context

• Identify and correct sentence fragments by ensuring every sentence contains a main clause with a subject and a finite verb.

Although the conditions were difficult. ❌ → Although the conditions were difficult, the team completed the survey. ✅

• Correct comma splices by separating with a full stop, adding a coordinating conjunction, using a semicolon, or restructuring with subordination.

The sample size was small, the findings were significant. ❌ → Although the sample size was small, the findings were significant. ✅

• Never use although and but together — choose one or the other.

Although the findings were significant, they need further verification. ✅

• Never use will in time clauses — use the simple present or present perfect.

As soon as the analysis is complete, the team will submit the findings. ✅

• Use whether — not if — in formal noun clauses as subject, after prepositions, and after be.

Whether the methodology is adequate has not been established. ✅

• Apply the bare subjunctive or should + bare infinitive after verbs and adjectives of recommendation and necessity.

It is essential that all data be archived within thirty days. ✅

• Ensure participial clauses attach to the correct subject — avoid dangling participles.

Studying the data, the researchers identified an anomalous pattern. ✅ (not the anomaly was identified)

• Choose present participle for active relationships; past participle for passive ones.

Scientists studying the ocean (active — scientists do the studying) ✅ Data collected by the team (passive — data is collected) ✅

• Apply parallelism when combining multiple elements in a list or series.

The team collected samples, analysed the data, and published the findings. ✅

• Vary sentence structure — short sentences for emphasis, longer ones for elaboration and qualification.

Scientists have been studying hydrothermal vent ecosystems for nearly fifty years. The full picture remains incomplete. ✅ (contrast of long and short)

4. Common Errors and Corrections

5. Lesson Mastery

After completing this lesson, you should now be able to:

    ✅ Identify all the major categories of error in clause and sentence structure

    ✅ Understand the grammatical and communicative principles underlying each correction

    ✅ Apply accurate sentence structure across all clause types and combining strategies

    ✅ Avoid the most persistent errors in both production and analysis