One of the questions I hear most often in class is this:
“Teacher, why is it interested in Science but good at Mathematics? Why can’t I just use another preposition?”
It is an excellent question because it highlights one of the most misunderstood areas of English grammar: Prepositional complementation.
Unlike grammar rules such as subject-verb agreement (She walks vs They walk) or verb tenses (eat vs ate), there is no universal rule that tells us which preposition follows a particular word. Instead, every verb, adjective and noun has its own preferred grammatical pattern.
Linguists call this prepositional complementation, or more specifically, lexically-governed prepositions.
What Is Prepositional Complementation?
Every lexical item (a word stored in our mental dictionary) contains grammatical information.
For example, the adjective interested does not simply mean “curious”. It also carries a grammatical requirement:
interested + in + noun / gerund
Similarly,
good + at
capable + of
responsible + for
depend + on
The preposition is part of the word’s grammatical identity.
It is not something we can choose freely.
Why Is This So Difficult?
Most grammar follows rules.
For example,
Singular subject → singular verb
Plural subject → plural verb
Simple.
Prepositional complementation is DIFFERENT.
Take a look at these examples:
- good at
- interested in
- afraid of
- proud of
- responsible for
- succeed in
Can you see a logical pattern? Probably not.
That’s because there isn’t one.
These combinations developed naturally over centuries of language use and became fixed through convention rather than logic.
Even Similar Words Behave Differently
This is where many students become confused.
Study these sentences:
I specialise in preparing students for the PSLE.
I have expertise in preparing students for the PSLE.
She is an expert at solving difficult problems.
All three sentences refer to knowledge and skill.
Yet the prepositions are different.
This happens because every lexical item has its own subcategorisation frame.
In linguistics, subcategorisation refers to the grammatical information stored with each word.
For example:
a) specialise (Verb)
Requires → PP headed by in
b) expertise (Uncountable noun)
Requires → PP headed by in
c) expert (adjective)
Requires → PP headed by at when followed by an activity.
Notice something?
Even though these words belong to the same semantic family, they do not necessarily share the same grammatical pattern.
Why “I have an expertise at…” Is Wrong
Students sometimes write:
I have an expertise at preparing students. (Wrong)
There are actually two grammar mistakes here.
1) expertise is an uncountable noun.
Just like:
- information
- advice
- knowledge
we do not say, “an expertise”
Instead, we say
“expertise” or “extensive expertise”
Secondly, the noun expertise collocates with in, not at.
Therefore, the correct sentence is:
I have expertise in preparing students for the PSLE.
Why Native Speakers Rarely Make These Mistakes
Here’s something interesting. Ask a native English speaker why we say
interested in
instead of
interested at
Most of them cannot explain it. They simply know it sounds correct. Why? Because they acquired these patterns through implicit learning.
From childhood, they repeatedly heard, “interested in”, thousands of times. Eventually, the entire phrase became stored as one mental unit. This is exactly how language acquisition works.
Why Singapore Students Find This Difficult
Singapore students often try to apply logic.
For example, “If I can be good at something, why can’t I also be interested at something?”
Unfortunately, English does not work this way. Prepositions are largely based on collocation, not reasoning. In fact, this is one of the most frequently tested grammar concepts in Singapore schools. Recent PSLE grammar resources continue to feature questions that require students to distinguish between similar-looking prepositional phrases and choose the one that fits the sentence accurately.
Likewise, authentic prelim papers from many Singapore primary schools consistently assess students on grammar MCQs, grammar cloze, editing and synthesis & transformation, where accurate collocations and prepositions are essential for scoring well.
Don’t Memorise Words. Memorise Chunks.
This is one philosophy we emphasise at Writers Studio.
Many students memorise vocabulary like this:
- interested
- responsible
- succeed
- depend
Unfortunately, they have only learnt half the language. Instead, memorise the complete chunk.
- interested in
- responsible for
- succeed in
- depend on
- capable of
- specialise in
When you learn language in chunks, you stop asking, “Which preposition should I use?” Instead, the correct phrase comes naturally because your brain has already stored it as one complete unit.
Why This Matters for the PSLE
Many parents assume prepositions are only tested in Grammar MCQs. In reality, they appear throughout Paper 2.
Students encounter them in:
- Grammar MCQ
- Grammar Cloze
- Editing
- Comprehension Cloze
- Synthesis & Transformation
One incorrect preposition can cost valuable marks even if the rest of the sentence is perfect. This is one reason why top-school prelim papers devote significant attention to collocations and fixed grammatical patterns.
Finally, prepositional complementation is difficult because it belongs to the lexicon, not to general grammar. Each word stores its own grammatical “instructions”, including which preposition may follow it. Since these pairings are based on convention rather than logic, they cannot always be deduced from first principles.
The good news is that there is a smarter way to learn them. Instead of memorising isolated vocabulary, memorise collocations. Don’t learn interested. Learn interested in.
Don’t learn depend. Learn depend on.
Don’t learn responsible. Learn responsible for.
This simple change in learning strategy mirrors how fluent speakers mentally organise language. Over time, these combinations become automatic, making your child’s grammar more accurate, their writing more natural, and their performance in English much stronger.
