We’re used to seeing noun and adjective phrases as subject complement, like in these sentences:
My hobby is collecting vintage stamps.
The soup tastes incredibly delicious.
But clauses too can occupy subject and object complement position. Such clauses can be finite (noun clause) or non-finite (gerund phrase and infinitive phrase).
1. Subject complement
1.1. Finite clause as subject complement
Although we usually study noun clause as one broad unit, they can be divided into three types:
- That-clause, which are introduced by that
- Wh-interrogative clause, which are introduced by wh-elements (how, when, where, why, who, whom, whose, what, and which)
- Yes–no interrogative clause, which are introduced by if and whether
Of these, noun clauses introduced by that, wh-elements, and whether can function as subject complement in a sentence. You can usually drop that in that-clause. Examples:
The problem is that we have run out of money. [The problem is we have run out of money is fine too]
The government’s concern is how the new policy would be implemented.
The key factor in sowing crops this year is when the rain arrives.
Our new office is where a shopping mall existed earlier.
The question is why you left without informing anyone.
What’s still unknown is who will be the next head coach. [Another wh-clause occupies subject position]
The question no one is asking is whom should this responsibility be entrusted to.
The dilemma is whose plan should be followed.
The electrical fault is what sparked the fire.
What security force can’t seem to decide is which route to take. [Another wh-clause occupies subject position]
The issue with this plan is whether it involves any unforeseen assumptions.
1.2. We’re not done with finite clause yet
If you’re an intermediate to advanced learner, you would’ve been exposed to the three types of noun clauses we covered earlier. But if you’re an advanced plus learner, if there is such a term, you would know that there are two more – exclamative clause and nominal relative clause. Since they too function nominally, in common use, they are lumped together with the three we’ve covered so far under one big umbrella of noun clause.
Here are few (not all introductory words have been covered) examples of nominal relative clause as subject complement. (Exclamative clause can’t function as subject complement.) Note that they share some introductory words with wh-elements.
The plan is whatever works best.
The teacher is whoever is most qualified.
The spokesperson will be whomever the team chooses.
The final choice will be whichever you prefer.
We covered some distance with finite clauses as subject complement. Here is a summary:
| Type of finite nominal clause | Does it function as subject complement? |
| That-clause | Y |
| Wh-interrogative clause | Y |
| Yes–no interrogative clause (If) | N |
| Yes–no interrogative clause (Whether) | Y |
| Exclamative clause | N |
| Nominal relative clause | Y |
Note: For a finite clause that has multiple introductory words, some introductory words may not lead to natural and idiomatic subject complement.
1.3. Non-finite clause as subject complement
There are two types of nominal non-finite clauses, also called nominal phrases:
- Nominal to-infinitive clause (also called infinitive phrase)
- Nominal -ing clause (also called gerund phrase)
Both can function as subject complement in a sentence. Examples:
The fastest way to profitability is to reduce cost.
The company’s mission is to reach 10 GW of solar capacity.
The key to success is maintaining positive attitude and working hard.
Her passion remains teaching young children.
Besides, we have a variant of nominal to-infinitive clause, derived from the finite clauses we covered earlier:
- Infinitive wh-clause derived from wh-interrogative clause
- Infinitive whether-clause derived from yes–no interrogative clause
(Note that if and that can’t introduce a to-infinitive clause.)
They function much like their parental clauses, though with some restrictions. Why, for example, is rarely used in infinitive form. Here are examples of few infinitive wh-clause and infinitive whether-clause as subject:
The problem is how to achieve the target with such low budget.
The issue is when to release the movie.
The main point is where to set up the new office.
The consideration is whom to appoint as the next sales head.
The challenge is what to focus on first.
The point still under discussion is whether to continue the research.
Here is a summary of non-finite clause as subject complement:
| Type of non-finite nominal clause | Does it function as subject complement? |
| To-infinitive clause | Y |
| Infinitive wh-clause | Y |
| Infinitive whether-clause | Y |
| -ing clause | Y |
Note: For a non-finite clause that has multiple introductory words, some introductory words may not lead to natural and idiomatic subject complement.
In this post, we’re learning clauses in subject complement and object complement position. You can learn clauses in other positions here:
2. Object complement
2.1. Finite clause as object complement
None of that-clause, wh-interrogative clause, or yes–no interrogative clause can be object complement in a sentence.
2.2. We’re not done with finite clause yet
Only nominal relative clauses can function as object complement. Examples:
The critics called the film what everyone had hoped for.
We painted the room whichever color the interior designer suggested.
They named the dog whatever their children wanted.
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2.3. Non-finite clause as object complement
Non-finite clauses don’t take this position.
