Clefting in English, or “What the Point Is... Is That…” vs. “The Point Is.. Is That…”?
- Galina Blankenship
- Apr 4, 2022
- 18 min read
Updated: Apr 7, 2023
Topics, Topic-Shifting, and Topic-Marking in Languages
In English, intonation plays a key role in assigning prominence to constituents within sentences—more so than in French, for example, where prominence tends to be a property of specific phrasing, or in Turkish, in which emphasis often depends on a particular ordering of words within a sentence. This means that in writing, when we cannot use intonation, indicating sentential stresses must rely on visual cues only.
Some languages (Japanese, Korean, Classic Chinese, etc.) use special markers to signal the topic of a sentence, a constituent that generally occurs at the beginning and indicates what the sentence is about. For example, in Japanese, topics are indicated by a postpositional particle -wa placed after the topic-element.
Turkish has devised certain topic-shifting devices: the postpositional clitic ise or the converbial construction gelince that signal shifting to new topics. Although bearing no stress, the clitic ise is able to pre-stress any word that precedes it. Other Turkish clitics, such as da(de) or bile, when placed after the initial word(s) in sentences, effectively act as pre-stressers. The English equivalent topic-marking construction is as for ... :
Ben ise evde kaldım.
As for me, I've stayed at home.
In both Turkish and English, the topicalized elements are often marked with a distinctive comma intonation in speech or an introductory comma in writing. Therefore, one can argue that the introductory comma in both languages functions as a topic-marker. Topicalized elements range from subjects and objects to adverbials and discourse connectives (as shown below):
Önceleyin, karşıdaki koca Stanköy Adası’nı görmez oldum.
At first, I stopped seeing the large island of Stanköy that was across me.
Halikarnas Balıkçısı, Bütün Eserleri: 1
Cleft Constructions
In addition to the topic-marking construction as for ..., English has also devised special constructions called clefts or cleft sentences to unequivocally signal the elements in sentences that need emphasizing. The term cleft (from cleaving) suggests the mechanism of creating cleft structures, i.e., by cutting or cleaving a single clause in two and stitching the two parts together again in different arrangements.
By definition, clefts are a writing convention, and as such, many of them are rather formal in tone. Nonetheless, some clefts have become part of the English idiom, used in both formal and casual speech.
Generally, a cleft sentence is a special kind of complex sentence (consisting of a main and dependent clause), whose main purpose is to divide a sentence into two parts: an emphasized part (in most cases, a contrasting topic) and de-emphasized part, with a clear boundary and distinction between the two parts.
In written English, this arrangement is particularly useful, since we cannot use intonation to mark emphasis or the boundaries of the emphasized part. In speech, the boundary between the two parts is often used as a place to take a pause (that may sound like hesitation) and recuperate, especially before the focused part that requires more effort to utter.
Four Types of Cleft Constructions
There are two basic and two variation types of cleft sentences:
1. It-clefts
2. Wh-clefts
3. Reverse wh-clefts
4. Demonstrative this-clefts
1. It-clefts utilize yet another construction in English, the so-called dummy it-subject, to draw attention to a constituent placed after the it-subject. It-clefts typically emphasize subjects and objects, as well as place and time adverbial phrases and clauses:
Our mother is cooking the Christmas dinner in our kitchen.
It is our mother that is cooking the Christmas dinner in our kitchen.
It is the Christmas dinner that our mother is cooking in our kitchen.
It is in our kitchen that our mother is cooking the Christmas dinner.
By displacing the subject to the end of the clause, it functions as a placeholder for the content moved to the end of the clause.
2. In the wh-type cleft constructions, constituents are fitted into a complex nominal sentence to draw attention to its subject constructed as a nominal wh-clause (sentential subject):
What our mother is cooking in our kitchen is the Christmas dinner.
3. The reverse wh-clefts do exactly what their name suggests: they reverse the ordering of the two wh-clausal parts:
The Christmas dinner is what our mother is cooking in our kitchen.
4. The demonstrative this-clefts begin with the demonstrative pronouns this or that instead of it or wh-word. They are often used in speech:
You see that villa? That’s what I’d like to buy.
This is what I mean!
It-Clefts: Focusing Device
It-clefts are complex sentences (with a main and a dependent clause) that are used to emphasize a particular constituent. They are formed from regular sentences (e.g., I love you) by splitting the sentence into two halves (e.g., I love | you):
1) The first half is structured as a simple nominal sentence (linked with the verb be) with the introductory dummy it-subject and a complementary predicative.
2) The second half is a complementary that- or wh-clause. An it-cleft thus has two complements structured into its construction: the first is a nominal complement that receives a strong focus-stress, while the second one is a that- or wh-complement that presents some sort of presupposed information:
I love you.
⇓
It + is + [you] + that + [I love]
⇓
It is you that I love.
Alternatively, with animate subjects, that can be replaced with who:
It is [you] whom [I love]. It is [you] who [I love].
formal informal
It-Clefts: Information Structure
Consider these exchanges with it-cleft sentences:
A: Do you love her? A: Are you going to marry Susan?
B: No, it’s you that I love. B: No, silly! It’s you that I love!
In both exchanges, the focus falls on you. The adjacent that-clauses, however, may have different interpretations: in the first exchange, it seems to represent backgrounded old information (backgrounded topic), whereas the second that-clause presents backgrounded new information (backgrounded focus). In either case, the that-clause represents presupposed, post-focused, de-emphasized information.
It-clefts should, therefore, be understood contextually. They are often constructed for a pragmatic purpose, with an emphatic discourse coded into them.
It-Clefts: Three Main Uses & Stressing Patterns
It-clefts have the following uses, depending on the distribution of given (old) and new information in the sentence to:
▼ Contradicting or contrasting (with the focused position containing contrastive new information (contrastive topic) and the that/who-clause, backgrounded old information (old topic):
A: Bob must have recommended him as department chairperson.
B: Actually, it was Betty [who recommended him].
new --old (backgrounded topic)--
▼ Arguing a point (with the focused position containing contrastive old information (contrastive topic) and the that-clause, new information (presentational topic)):
A: But why is shape of the wing so important?
B: It is [the shape that determines the maximum speed].
old --------------------new information--------------------
▼ Establishing a topic to be elaborated (with the entire sentence containing new information (presentational topic)):
[It was just about 90 years ago that Henry Ford gave us the weekend].
-----------------------------------new information----------------------------------
It-Clefts: Focusing Any Element Except Verbs
The focused constituent in an it-cleft is often a noun phrase:
It was John who spoke to Bill. It was last year that he got promoted.
However, it can also be, a prepositional phrase, an adverbial phrase, a nonfinite clause, a gerund, or an adverbial clause:
It was not [for the bonus] that [we worked so hard]. It was [greedily and speedily] that [Bill drank his beer].
prepositional phrase adverb
It is not [to make life easier] that [we’re making the rules]. It could be [leaving the office] that [the boss reacted to].
infinitival clause gerund-clause
It was in September that he first found out about it. It was with great reluctance that Maria accepted the invitation.
time adverbial phrase manner adverbial phrase
In it-cleft sentences, emphasis may be thrown upon any part of the sentence that can potentially be a complement. This means, therefore, that predicates (finite verbs), which function as heads to complements, can never be focused in it-cleft sentences.
Focusing of Pronominal Subjects
When the emphasized subject is a pronoun, we can use either of these constructions. Note the number agreement between the subject and verb:
It is I who am responsible. It's me that's (who's) responsible.
formal informal
It is you who are in the wrong. It's you that's in the wrong.
formal informal
Paraphrasing can help avoid confusion:
I'm the person who's responsible. I'm the one who's responsible.
Focusing of Topics
The topic in it-clefts is often contrastive:
It’s the other book, not this book, that I want to read.
The verb be in it-cleft sentences can be negated, in which case, the first negative part is contrasted with the second positive part:
It’s not low pay that we object to, it’s the extra responsibilities.
Focusing of Not
It is not that they wanted to move here: It's just that they need a change.
Focusing of Prepositional Phrases
Karl was always there to help her, and it was to him that she now turned for support.
Focusing of Adverbial Clauses
It is because he was worried that he called you. It wasn’t until we arrived at the hotel that we met them.
adverbial reason because-clause adverbial temporal until-clause
It was only when I read her letter that I realized what was happening.
adverbial temporal when-clause
Focused adverbial clauses can also be used as main clauses in complex adverbial sentences:
If he wants to be a lawyer, it is because he wants to make a lot of money.
▶ Cleft-Focusing Test ◀
The focusing ability of it-clefts is a useful tool for distinguishing integral (essential) adverbial clauses from peripheral (loosely related) ones.
 | In English, some subordinating conjunctions (since, as, when, while), in addition to their primary integral uses (as adverbial time-clauses), have historically acquired secondary (and even tertiary) uses, which are peripherally (semantically less closely) related to the main clause’s event. For example, both since- and as-clauses have the secondary uses as reason clauses (since/as the weather was fine, we held the party outside); the when-clause, as a concession clause (He gave me a beer, when what I’d asked for was a shandy); and the while-clause, as a contrast clause (My children enjoy jazz, while l prefer classical music). |
The difference between the integral and peripheral uses is perfectly illustrated by because- and since-reason clauses.
Because-clause below is integral, as it informs us for the first time of the reason for the main action:
He called you [because he was worried].
Topic Focus
With since instead of because, the adverbial clause loses its emphasis and reads as a reminder of the reason for the main action (i.e., as a backgrounded topic):
He called you, [since he was worried].
Focus Backgrounded Topic
We can verify this backgrounding aspect of the since-clause by using the it-cleft focusing test:
It is because he was worried that he called you.
* I̶t̶ ̶i̶s̶ ̶s̶i̶n̶c̶e̶ ̶h̶e̶ ̶w̶a̶s̶ ̶w̶o̶r̶r̶i̶e̶d̶ ̶t̶h̶a̶t̶ ̶h̶e̶ ̶c̶a̶l̶l̶e̶d̶ ̶y̶o̶u̶.̶
The primary use of since is temporal, which means that it should be able to focalize:
He has not spoken to us [since his wife left him].
It is [since his wife left him] that he has not spoken to us.
It-Cleft Idiomatic Variations
All-Clefts
All (that) she wanted to buy was a few books.
There-Clefts
There seemed to be nothing that we could do. There goes my hope for a better future.
There comes a time when you have to do something. And then there’s this man that she met online.
It-Clefts: Pragmatics of Presupposition
As shown above, one of the most common uses of it-clefts is to contrast with any previously presented information.
It-clefting can represent a unique stressing pattern: While the first part (it + [be] + focus) is contrastively focused, the second part (that-clause) can read like a reference to an old or given topic (meaning, a backgrounded topic). In speech, such presupposed information is clearly distinguishable thanks to its falling intonation and a dramatic pitch drop.
Reading aloud an exchange involving a contrastive it-cleft construction easily reveals this intonational pattern:
1. The more stressed the focused part is (in bold), the more de-stressed the backgrounded part is (in italics):
A: Did you hear? Lea bought the car from Olav.
B: No, it was Olav that bought the car from Lea.
2. If the focused part is not overtly contrastive or contradictory, the emphasis will be toned down and the sentence, more balanced, even though the second part will still have a lower pitch than the focused part:
It was to show how much I cared for her that I bought her the necklace.
I don’t mind her criticizing me, but it’s how she does it that I object to.
The de-stressing intonation of presupposed information can be easily explained: A presupposed proposition is regarded by the speaker as a given truth, or something that is so evident that requires no additional intonational effort. The boundaries of the backgrounded part are markedly low pitch, reflecting the speaker's switching to the energy-saving mode.
This is possibly the key to understanding the nature of utterances as intonational units. Since the sound-producing aspect of speech operates by energy sourced in the physical capacity of our lungs, each utterance or sentence we make is essentially a thermodynamic enclosed system.
Just as a thermodynamic system deals with the transfer of energy (which can never be created or destroyed, but only converted) from one place or form to another, so do we when each time we push through an utterance the finite amount of energy we have in our lungs. Without any pre-thought, we nonetheless know how to distribute that energy within a sentence, whether by spreading it evenly or by choosing the part to apply most of the illocutionary force, while letting the rest be low-energy.
It-Cleft Clause vs. Relative Clause
The that-clause within it-cleft constructions is hard to define. Syntactically, it resembles an essential relative clause. This resemblance can cause ambiguity:
Cleft Clause:
A: Was it a bookshelf that we got from Ann?
B: It was the vase that Ann gave us. [= It was the vase, and not a bookshelf, that Ann gave us]
marked focus
Relative Clause:
I heard the glass break. It was the vase that Ann gave us. [= It was the vase that was given to us by Ann.]
non-marked focus
To avoid this ambiguity, no other wh-words, save for that and who, should be used with it-clefts:
A: How did he manage to save the firm? Did he cut his staff and make it profitable?
B: No, it was by improving distribution that he made it profitable.
B: N̶o̶,̶ ̶i̶t̶ ̶w̶a̶s̶ ̶b̶y̶ ̶i̶m̶p̶r̶o̶v̶i̶n̶g̶ ̶d̶i̶s̶t̶r̶i̶b̶u̶t̶i̶o̶n̶ ̶h̶o̶w̶ ̶h̶e̶ ̶m̶a̶d̶e̶ ̶i̶t̶ ̶p̶r̶o̶f̶i̶t̶a̶b̶l̶e̶.̶
A: Was he ill? Is that why you returned?
B: It was not because he was ill that we decided to return.
B: I̶t̶ ̶w̶a̶s̶ ̶n̶o̶t̶ ̶b̶e̶c̶a̶u̶s̶e̶ ̶h̶e̶ ̶w̶a̶s̶ ̶i̶l̶l̶ ̶w̶h̶y̶ ̶w̶e̶ ̶d̶e̶c̶i̶d̶e̶d̶ ̶t̶o̶ ̶r̶e̶t̶u̶r̶n̶.̶
Unlike relative clauses, which either define or describe their related noun heads, it-clefts identify (point to) their noun heads.
In it-clefts, it has no reference outside the sentence, whereas in relative clauses, it is a pronoun typically referring to a previous discourse:
A: Who is your boss? A: Is it Mr. or Mrs. Blake who has been appointed?
B: It is Mr. Blake—who has just been appointed. B: It is Mr. Blake who has just been appointed.
It refers to your boss in the preceding question. It doesn't refer to anything (save for its copy in a previous sentence).
Compare:
Cleft Clause (formal): OR Cleft Clause (less formal):
It was in Warsaw that the film was made. It was in Warsaw where the film was made.
[= And not in Kraków.] [= And not in Kraków.]
Nonessential Relative Clause:
It was in Warsaw, where the film was made.
[= It happened in Warsaw, and by the way, the film was made there.]
Cleft Clause (formal): Cleft Clause (less formal):
It was in the city that the film was made. OR It was in the city where the film was made.
[= And not in the village.] [= And not in the village.]
Essential Relative Clause: OR Nonessential Relative Clause:
It was in the city where the film was made. It was in the city, where the film was made.
[= In which city?] [= Where was it?]
Wh-Clefts (Pseudo-Clefts): Sentential Clauses
Like an it-cleft sentence, wh-clause can be used to highlight one element for contrast, with the focus falling outside the wh-clause:
We need more time. It is [more time] that [we need].
simple sentence if-cleft
[What we need] is [more time]. [More time] is [what we need].
wh-cleft reversed wh-cleft
It can be either subject or complement of the verb be, although the subject position is more common, which is why it is also referred to as a nominal relative clause:
Both wh- and it-clauses can imply a contrast:
We don’t need more money—what we need is more time.
Wh-clefts are formed from regular sentences by adding what at the start and be before the focused information. This way, we can focus attention on certain information in a sentence:
A: What did Vera buy? Was it a fantasy collection?
B: What Vera bought was a poetry collection.
Elements that can be focused include noun phrases, infinitive complements, interrogative complements, gerund complements, and verb phrases:
What [she wanted] was [a glass of milk]. What [he promised] was [to have it today].
nominal complement infinitival complement to-clause
What [I don't know] is [why they decided to do it today]. What [I really dislike] is [listening to nonsense].
interrogative complement gerund complement
What [he does] is [sell cars].
verbal complement
If the information in focus is a noun phrase, no connective needs to be used:
What I’d like you to work on is [the revision exercise on the website].
noun phrase complement
A: We’ve only got this small bookcase—will that do?
B: No, what I was looking for was [something much bigger and stronger].
noun phrase complement
However, if the focused element is a clause, we need to use that to connect it:
Isa was two hours late: what had happened was that [his bicycle chain had broken].
complement that-clause
Uses of Wh-Clefts: Main Uses & Stressing Patterns
Wh-clefts, in which new information is generally in the focused position, are used especially in conversation for:
▼ Resuming a topic temporarily relegated to the background:
A: Well, they served us some kind of white beverage in these interesting-looking bowls.
B: What kind of bowls?
A: They were all covered with beautiful colors and designs. Well, what I didn't realize at the time was that the beverage was alcoholic.
▼ Presenting the gist of preceding conversation:
A: If I go there, my mom will be asking me what I am doing with myself. And then both my mom and my dad will start to ask me why I don't have a steady job yet.
B: So, what you're saying is that they will never get off your case.
▼ Contradicting something that has been said and possibly presenting an alternative explanation:
A: People reach retirement age, they usually slow downs and become less interested in things like physical appearance and lifestyle.
B: Actually, what often happens is that older people become more interested in regaining some of their youthful appearance and lifestyle.
▼ Clarifying a possible misunderstanding or an imperfect understanding:
A: So, I was wondering if you could lend me a DVD.
B: A DVD?
A: You have a lot of DVDs, don’t you?
B: Yes, I do. What I meant was which DVD do you want?
▼ Expressing the speaker's stance, or attitude, regarding something in the conversation:
A: So, I guess you'll be happy to start drawing your Social Security check. You’ve looked into it, I suppose?
B: Yeah. What surprises me is that the amount you get actually goes up every year.
Wh-Clefts: Subject–Verb Agreement
A wh-clause is normally considered to be singular: if it begins a cleft sentence, it is followed by is or was.
However, in informal style, a plural copula verb may be used with plural nouns:
What we want is your loyalty.
your loyalty = singular
What we want is some of those cakes.
formal
OR
What we want are some of those cakes.
informal
Wh-Clefts: Focusing of the Predicate
While (by definition) it-clefts do not allow predicate focusing, wh-clauses do.
If you want to focus attention on someone's action, the sentence can be constructed with the complement taking the form of a nonfinite verb: a gerund or an infinitive (with or without to):
What I really dislike is listening to nonsense.
What he will do is sell cars. What he's done is spoil the whole thing.
What he will do is to sell cars. What he's done is to spoil the whole thing.
What John did to his suit was ruin it. What I'm going to do to him is teach him a lesson.
What John did to his suit was to ruin it. What I'm going to do to him is to teach him a lesson.
What he promised was have it today.
What he promised was to have it today.
Getting Rid of Long Subjects: Complements with Reason, Problem, Question, Idea
English default word order is Subject–Verb–Object, with these constituents making up the core of the English sentence. This means that our understanding of a sentence depends on how quickly and easily we get to the sentence’s core. In other words, the closer these elements are to the start of the sentence as well as to each other, the better.
This underlines one of the defining stylistic characteristics of the English language: English is averse to long subjects, strongly preferring lighter subjects to ensure the shortest distance between the subject and the verb.
Subject Complements: Wh- & That-Clefts
Cleft structuring can be applied to complement that-clauses as well, even though they sound rather awkward though:
That both defendants were lying was obvious to everyone in the courtroom. But this does not necessarily mean that both defendants were lying.
Oskar Garstein, Rome and the Counter-Reformation in Scandinavia
Likewise, wh-clefts are by definition heavy sentential clauses. Instead of starting a sentence with a long that- or what-clause, English starts with an introductory noun that summarizing the gist of the clause (e.g., fact, idea, question, reason, question, reason, point, thing, etc.), which functions as the subject, and packaging the rest as its complement:
That we'll meet soon feels me with joy. That they are fair I can testify.
The fact that we'll meet soon feels me with joy. The fact that they are fair I can testify.
The idea that we'll meet soon feels me with joy.
The notion that we'll meet soon feels me with joy.
Where you should play football is the playground, not the classroom.
The place that you should play football is the playground, not the classroom.
(The place where you should play football is the playground, not the classroom.)
Whom I enjoy reading is Peter Carey. When I work best is early morning.
Somebody that I enjoy reading is Peter Carey. The time that I work best is early morning.
(Somebody who I enjoy reading is Peter Carey.) (The time when I work best is early morning.)
If the complement is a clause, then use that to connect it:
What we hope for is that this time all parties will cooperate.
Our hope is that this time all parties will cooperate.
The reason is ..., The fact is ..., The problem is ...
English has a number of such idiomatic expressions. One of the most common of them is:
The reason is … / The reason is (that) …
Effect (Clause) | ʙᴇ | Reason (Phrase) |
The reason for not finding a job | is | the weak economy. |
Effect (Clause) | ʙᴇ | Reason (Clause) |
The reason (that) he can't find a job | is | that the economy is weak. |
Effect (Phrase) | ʙᴇ | Reason (Phrase) |
The reason | is | the weak economy. |
Effect (Phrase) | ʙᴇ | Reason (Clause) |
The reason | is | that the economy is weak. |
The variant with that(s) is more formal:
The reason (that) I left the party early was that I was feeling unwell.
formal
In informal speech, speakers often add repetitive pronouns and conjunctions (why and because), which are not incorrect but redundant:
The reason why I left the party early was that I was feeling unwell.
less formal
The reason why I left the party early was because I was feeling unwell.
informal
Other expressions include:
The problem is (that) …
Out biggest problem is that we don't have enough resources to make this film.
The fact is (that) …
The fact is that a happy person makes a better worker.
The answer is (that) …
The answer is simply that they are interested in doing it.
The explanation is (that) …
The most favored explanation was that he was finally getting tired.
The thing is (that) …
The thing is that I don't know why they decided to do it today.
Prepositional Phrases
When specifying a reason, solution, problem or important point, a prepositional phrase is commonly used to modify the noun. Choice of preposition may vary:
for of
The main reason for the crisis is that … The point of this conversation is that …
The logic for this is that … The disadvantage of this is that …
The idea for this legislation is that … The benefit of this is that …
The concept for this idea is that … The result of this is that …
on/ about with
The current thinking on that is that … The problem with overspending is …
The current thinking about that is that … The understanding with them is …
The general feeling about the law is that …
The understanding about that is that …
The understanding on that is that …
to to/ of
The solution to the problem is that … The advantage to your method is …
The trick to fixing it is that … The advantage of your method is ...
The drawback to you ridea is that …
Object Complements
We had no idea how worried you were.
I wanted to know the real reason why you left.
I cannot think of a time when you disappointed me.
Reversed Wh-Clefts (Inverted Pseudo-Clefts)
Depending on the pragmatic or compositional context, we can put the wh-clause either at the beginning or the end of the sentence, in which case the reversed wh-cleft turns into an inverted pseudo-cleft:
What upset me most was [his rudeness]. [His rudeness] was what upset me most.
wh-cleft reversed (inverted) wh-cleft
In reserved wh-clefts, the focused information occurs at the beginning followed by [be] + what:
What I really need is a vacation. A vacation is what I really need.
wh-cleft reversed wh-cleft
Reverse wh-clefts display a wide variety of wh-forms: what, when, why, and how:
A poetry collection is what Vera bought. Vera was who bought a poetry collection.
Demonstratives This-Clefts
A common type of cleft-sentence in informal English is one in which a wh-clause is linked by the verb be to a demonstrative pronoun (this or that):
I had difficulty starting the car today. That’s what always happens when I leave it out in cold weather.
These sentences are similar to wh-clefts both in their structure and focusing effect, meaning that the focused part is typically sentence-final (in CAPS):
This is where I first met MY WIFE. This is how you start the ENGINE.
While in wh-clefts, the cleft variable (that is, the material encoded by cleft clauses) is typically given and its value (expressed by the cleft constituent) is new, this may be different in demonstrative clefts.
Neither of its elements may contain new information, as in the example below:
That is what I think, basically.
Yet in other examples, it is the sentence-initial cleft-clause that may contain the new part of the message:
And THAT'S when I got sick!
Are you trying to wreck my career? Because THAT'S what you’re doing.
Cleft-Forms in Sentences
All (that) she wanted to buy was a few books. And then there’s this man that she met online.
There seemed to be nothing that we could do. There comes a time when you have to do something.
There goes my hope for a better future. It was with great reluctance that Maria accepted the invitation.
It was because he was ill that we decided to return. It was in September that he first found out about it.
It is not that they wanted to move here: It's just that they need a change.
If he wants to be a lawyer, it is because he wants to make a lot of money.
Double Copula vs. Reduplicative Copula
Some cleft-constructions may pose two fascinating problems: the so-called double copula and reduplicative copula, both referring to the same instance of repetitive linking verb, like is is. The difference is that the former is a perfectly acceptable grammatical occurrence, whereas the latter is a definite error:
Double Copula: Correct!
[What his problem is] is [that he is too busy].
The sentence = Sentential subject + Linking verb (is) + Sentential subject complement (that-clause)
Reduplicative Copula: Wrong!
[His problem] is] is [that he is too busy].
The sentence = Phrasal subject + Linking verb (is) + Sentential subject complement (that-clause)
English is particularly sensitive to long subjects, which are always marked in speech, intonationally with a pause that follows the long subject. Therefore, a sentence with a sentential subject (i.e., a subject structured as a clause), a long noun phrase, or a noun with extensive post-modification would have an intonational boundary (rising intonation and a pause) marking the subject.
On the other hand, in English equative clauses (with copula predicate), the copula marks the boundary between the subject area and the verb area. So, one may speculate that, when the speaker uses a wh-cleft as the subject, she pauses (or hesitates) after the wh-clause, which is where the end of the long subject, the boundary between the two parts of a cleft sentence, and the boundary between the subject area and the verb area merge:
What his problem is … is that he is too busy.
As it happens, this doubling of copula is grammatically fine.
One may speculate that the similarity between wh-clefts and complex sentences with non-clausal nominal subjects confuses speakers. As they reach the first is, they may pause:
His problem is … is that he is too busy.
Forgetting that a verb has already been used and because the clause after is starts with the complement that-clause, speakers may repeat the verb, causing an erroneous reduplicative copula. What speakers do is essentially treat the clause His problem is as the subject of the sentence as a whole, and not the subject + predicate, proceeding to forge ahead with another copula-verb.
Similar structures with reduplicative copula:
The reality is … is that …
My point is … is that …
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