Relative and Participle Clauses: Packing More into a Sentence

At C1 the difference between competent and fluent English is often density: how much you can attach to one noun without starting a new sentence.

Defining vs non-defining

Defining — tells you which one. No commas.

The report that we published in June has been withdrawn.

Remove it and you no longer know which report. The information is essential.

Non-defining — adds extra detail. Commas required.

The report, which we published in June, has been withdrawn.

There is only one report; the clause just adds a fact. The commas change the meaning, and this is the single most common C1 punctuation error.

My brother who lives in Berlin is a doctor. (I have several brothers.)

My brother, who lives in Berlin, is a doctor. (I have one.)

Two rules follow: that cannot be used in non-defining clauses, and non-defining clauses can never be reduced.

Dropping the pronoun

In a defining clause, if the pronoun is the object, you can drop it:

The book (that) I ordered hasn't arrived. ✅ (object — droppable)

The book that arrived was damaged. ✅ (subject — cannot drop)

Quick test: if a noun or pronoun follows immediately, it was the object, and you can drop it.

Prepositions

The colleague who I spoke to. (informal)

The colleague to whom I spoke. (formal — the preposition moves to the front and forces whom)

Never to who. Once the preposition is fronted, whom is obligatory.

Whose, where, when

• the company whose licence was revoked (possession — works for things too)
• the year when the policy changed = in which
• the point where the argument fails = at which

Where and when are droppable in defining clauses, just like that: the day (when) we met · the place (where) we stayed.

Which for a whole clause

Non-defining which can refer back to an entire idea rather than a single noun — a structure that carries a lot of C1 commentary:

• He arrived an hour late, which didn't help.
• They cancelled without warning, which is exactly what I'd expected.

Note that only which does this. ❌ He was late, what annoyed everyone.

Quantifier + of whom / of which

Formal writing joins two facts about the same group with this pattern instead of a new sentence:

• We interviewed forty candidates, most of whom had no experience.
• The company runs six sites, two of which are due to close.
• She made several points, none of which were addressed.

Only whom and which work here — never who or that.

Reduced (participle) clauses

Defining clauses with a continuous or passive verb can lose the pronoun and auxiliary:

The people who are waiting outside → the people waiting outside

The measures that were introduced last year → the measures introduced last year

This is what makes formal English so compact:

Applicants submitting incomplete forms will be contacted.

Funds allocated to the scheme remain unspent.

Participles at the front of a sentence

The same forms open sentences, replacing because, after or while:

Form	Replaces	Example
-ing	while / because	Working from home, I miss the office.
Having + participle	after	Having finished the report, she left.
passive participle	because / when	Written in 1890, the book still sells.
Being + participle	because	Being new, he asked a lot of questions.

The trap: the participle must belong to the noun it sits next to.

❌ Having reviewed the data, the conclusion was obvious. (the conclusion reviewed nothing) ✅ Having reviewed the data, we found the conclusion obvious.

Why this is the C1 threshold — a B2 writer produces three short sentences where a C1 writer produces one. The information is identical; the difference is whether the reader has to reassemble it. Every clause you can attach to a noun is a sentence you don't have to start.

Compare the same content at both densities:

Three sentences	One
We published a report in June. It recommended six changes. Two of them have been adopted.	The report we published in June made six recommendations, two of which have been adopted.

Test yourself

The quiz below covers commas, droppable pronouns, fronted prepositions and reduction.