About Essential Part
An essential part question names a thing and four of its parts, of which exactly one is a part the thing could not be without. The other three are there because they are what one pictures when the thing is mentioned - a bell on a bicycle, a rider on it, a path under it - so the question tests whether a part can be told from a companion. Some rows admit argument, and this page is honest about that: one answer is recorded for each, and every explanation says why that answer rather than another.
What you need to understand
- The question asks for the necessary part. Remove the option and ask whether what is left can still be called by the same name. If it can, the option is not essential.
- Four things are commonly offered instead of the essential part. Something that usually accompanies the thing; something that is an instance of it; something that improves it; and something that is needed to make it work well rather than to make it what it is.
- An option can be entirely true and still not be the answer. A bicycle usually has a bell is true, and a bell is not part of what makes a bicycle a bicycle.
- A part that does the same job as another is not essential as that part, though the function may be. A window needs an opening, and glass is one of several things that can fill it.
- Where structure does not settle it, purpose often does. A clock is defined by measuring time rather than by having hands, because a clock without hands that still measures time is a clock.
- Where purpose does not settle it, structure does. A triangle is defined by having three straight sides, not by any use it might be put to.
- Instances are not parts. A particular bicycle is an example of a bicycle rather than a part of one, and the same is true of every named instance in the options.
- A consequence of being the thing is not part of its definition. A drawn triangle has three angles, which follows from having three sides, but the sides are what the definition names.
- An option that something else also has cannot be the answer, because it does not distinguish this thing from any other.
- The usual trap is association, which is the strength of one's mental picture of the object rather than an argument. Pictures are built from what is most visible and most mentioned, which is rarely what is essential.
- Where two options both seem essential, ask which of the two the definition of the thing could not be written without. The other is usually the stronger claim but the less necessary one.
- A part that can be absent while the thing remains itself is the answer to be rejected, however odd the thing looks without it.
- Because some rows admit argument, the way to use this topic is to read the explanation for each question rather than only the key. The recorded reason is the part worth learning.
How to work through these questions
- Read the four options and say what the thing would be without each one. Do this in the same order as the options so that the comparison is even-handed.
- Prefer the option that names what the thing does or what it is made of at the level of its definition, over one that names a material, a convenience or an accessory.
- Reject options that are instances rather than parts, and options that are consequences of the definition rather than parts of it.
- When two options are close, choose the one whose removal changes what the thing is called rather than only how well it works.
- Ask which option the definition could not be written without. The essential part is the one that appears in a careful definition and cannot be left out of it.
- Treat the explanation as part of the question. Where the row admits argument, the reason given is the useful thing to carry away.
Mistakes that cost marks
- Choosing what the thing usually has rather than what it must have, which is the mistake the three wrong options are built to invite.
- Choosing a part that improves the thing, such as a bell on a bicycle or a cover on a book.
- Being led by the mental picture of the object, which is assembled from what is most visible rather than from what is necessary.
- Treating a consequence of the definition as part of it, as with the angles of a triangle.
- Choosing something the thing shares with many other things, which therefore cannot be what makes it what it is.
- Mistaking a part of the thing's usual use for a part of the thing itself.
- Deciding by how technical or how familiar an option sounds rather than by removal.
- Forgetting that one answer is recorded for each question even where the row admits argument, and so arguing with the question instead of reading the explanation.
Worked example
Which of these is an essential part of a bicycle?
- Take the options one at a time and remove each in turn. A bell: the bicycle without it is still a bicycle, so the bell is not essential.
- A rider: a bicycle leaning against a wall is still a bicycle, so the rider is not part of it either. The rider is needed to ride it, which is a different thing from being part of it.
- A cycle path: a bicycle ridden across a field is still a bicycle, so the path is an accompaniment rather than a part.
- Two wheels that carry it along: remove the wheels and what is left is a frame and some pedals, which nobody would call a bicycle.
- All four options are associated with bicycles, and only one of them cannot be removed without changing what the thing is. The answer is the wheels.
Answer: Two wheels that carry it along
Practice questions with answers
A few Essential Part questions with the full solution shown, so you can see
how the method is applied before you attempt the timed set.
Question 1
Which of these must a proof have in order to be what it is?
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A
a set of symbols and signs
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B
a theorem that follows from it
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C
publication in a learned journal
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D
reasoning that shows a claim must be true
Answer: Option D — with explanation
What makes it a proof is that the reasoning compels the conclusion. A proof can be given in words, in symbols, or aloud.
The three that are not the answer are associated with it without being part of what it is, which is the distinction the question is testing:
- publication in a learned journal is associated with a proof but it is not part of what makes it what it is
- a set of symbols and signs is associated with a proof but it is not part of what makes it what it is
- a theorem that follows from it is associated with a proof but it is not part of what makes it what it is
Common mistakes
- this is associated with it rather than essential to it: a set of symbols and signs
- this is associated with it rather than essential to it: a theorem that follows from it
- this is associated with it rather than essential to it: publication in a learned journal
Question 2
Which of these is essential to a budget?
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A
a manager who checks it and approves the spending
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B
a plan for what will be received and spent
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C
a spreadsheet to keep it in
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D
an annual period it covers
Answer: Option B — with explanation
The plan is the budget. It can be kept in a notebook or in software, can cover a month or a year, and does not need anybody's approval to exist.
The three that are not the answer are associated with it without being part of what it is, which is the distinction the question is testing:
- a spreadsheet to keep it in is associated with a budget but it is not part of what makes it what it is
- a manager who checks it and approves the spending is associated with a budget but it is not part of what makes it what it is
- an annual period it covers is associated with a budget but it is not part of what makes it what it is
Common mistakes
- this is associated with it rather than essential to it: an annual period it covers
- this is associated with it rather than essential to it: a spreadsheet to keep it in
- this is associated with it rather than essential to it: a manager who checks it and approves the spending
Question 3
Which of these must a window have in order to be what it is?
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A
glass fitted into the opening
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B
a frame holding the glass in place
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C
an opening that lets light through
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D
a latch to keep it shut
Answer: Option C — with explanation
The opening is what a window is. Old windows were unglazed, and a shuttered opening was still a window; glass improves it rather than making it.
The three that are not the answer are associated with it without being part of what it is, which is the distinction the question is testing:
- a frame holding the glass in place is associated with a window but it is not part of what makes it what it is
- a latch to keep it shut is associated with a window but it is not part of what makes it what it is
- glass fitted into the opening is associated with a window but it is not part of what makes it what it is
Common mistakes
- this is associated with it rather than essential to it: glass fitted into the opening
- this is associated with it rather than essential to it: a latch to keep it shut
- this is associated with it rather than essential to it: a frame holding the glass in place
Question 4
Which of these is essential to a hypothesis test?
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A
a significance level of five per cent chosen in advance
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B
a decision rule based on the chance of the evidence
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C
a result published in a journal
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D
a sample large enough to detect it
Answer: Option B — with explanation
The decision rule is the test. Five per cent is a convention rather than a requirement, and the test can be run on a small sample, though with less power.
The three that are not the answer are associated with it without being part of what it is, which is the distinction the question is testing:
- a significance level of five per cent chosen in advance is associated with a hypothesis test but it is not part of what makes it what it is
- a sample large enough to detect it is associated with a hypothesis test but it is not part of what makes it what it is
- a result published in a journal is associated with a hypothesis test but it is not part of what makes it what it is
Common mistakes
- this is associated with it rather than essential to it: a result published in a journal
- this is associated with it rather than essential to it: a significance level of five per cent chosen in advance
- this is associated with it rather than essential to it: a sample large enough to detect it
Question 5
Which of these is essential to a queue in computing?
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A
items taken out in the order they went in
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B
a linked list to hold them
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C
a fixed size that cannot grow
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D
memory allocated in advance
Answer: Option A — with explanation
The order of removal is the defining property. It can be built on an array or on a linked list, and it can grow or be fixed in size.
The three that are not the answer are associated with it without being part of what it is, which is the distinction the question is testing:
- a fixed size that cannot grow is associated with a queue in computing but it is not part of what makes it what it is
- a linked list to hold them is associated with a queue in computing but it is not part of what makes it what it is
- memory allocated in advance is associated with a queue in computing but it is not part of what makes it what it is
Common mistakes
- this is associated with it rather than essential to it: a linked list to hold them
- this is associated with it rather than essential to it: a fixed size that cannot grow
- this is associated with it rather than essential to it: memory allocated in advance
Frequently asked questions
Are these questions not a matter of opinion?
Partly, and this page does not pretend otherwise. The line between a part and a companion is a real one, but a particular row can be argued. One answer is recorded for every question and the explanation gives the reason, so the disagreement can be had with the reasoning rather than with a black box.
What is the quickest test to apply?
Remove the option from the thing and ask whether what remains can still be called by the same name. A bicycle without a bell is a bicycle; a bicycle without wheels is not.
Why is a rider not an essential part of a bicycle?
Because the question is about the thing rather than about its use. A bicycle that nobody is riding is still a bicycle, so the rider belongs to the activity and not to the machine.
Should I look for purpose or for structure?
Either, whichever the definition cannot be written without. A clock is defined by what it does, so purpose decides it; a triangle is defined by what it is made of, so structure decides it. The question does not tell you which kind it is, so both have to be tried.
Where does this topic appear in a paper?
Usually inside the verbal reasoning section, and occasionally as a stand-alone item in general reasoning. The trap is always the same one: an associated part offered in place of a necessary one.
