Three adjectives that do not follow the regular pattern
Good, bad and far have special superlative forms that we learn separately: best, worst, farthest/furthest.
Learn them as ready-made pairs. Good, for example, has the superlative best. Do not add -est or most to best.
Of all the interns, Marco is the best at fixing printers.
Of all the interns, Marco is the best at fixing printers.
The best is a separate irregular form, rather than good with a changed ending.
That was the worst flight I've ever taken.
That was the worst flight I've ever taken.
The worst likewise is not formed by adding letters to bad.
Form: ready-made words rather than a word-building rule
A basic noun phrase uses the best solution or the worst result. But a possessive can replace the: my best friend. Learn both the adjective form and the structure of the whole phrase.
For physical distance, both farthest and furthest are possible. Their usage can differ in broader meanings; here we compare distances.
good → the best | bad → the worst | far → the farthest / the furthest
The best solution was also the cheapest one.
The best solution was also the cheapest one.
The best solution forms the subject noun phrase, with the.
Which village is the farthest from the railway station?
Which village is the farthest from the railway station?
The furthest from the railway station? would be equally correct.
Use: when the situation calls for a superlative
A superlative identifies an extreme within a group. The group can be established by of all, in the group, out of the three or the preceding conversation. Ties are also possible: These two are the best.
Without such a signal, the sentence can be ambiguous: the listener needs to understand that it compares within a group rather than simply describing an item’s quality.
Out of all the applicants, she has the best references.
Out of all the applicants, she has the best references.
Out of all explicitly establishes a group of several people.
This is the worst traffic jam this city has had in years.
This is the worst traffic jam this city has had in years.
In years suggests comparison with many previous cases.
Contrast: comparative versus superlative
Better, worse, farther and further are comparatives; best, worst, farthest and furthest are superlatives. A comparative compares two options or one against others: better than all the others. A superlative identifies an extreme within the group.
For two options, instructional writing normally favours a comparative: the better of the two. In everyday speech, best also occurs when choosing between two. The number alone is not enough to label a sentence incorrect.
Of the two laptops, this one has the better screen.
Of the two laptops, this one has the better screen.
The typical comparative better is used here to choose between two.
Of the five laptops in the shop, this one has the best screen.
Of the five laptops in the shop, this one has the best screen.
The superlative best identifies the top option among five items.
Where common errors come from
Learners often apply regular adjective patterns to good, bad and far: adding -est, as in goodest, baddest or farrest, or using most, as in the most good, the most bad or the most far.
Another error is double marking: adding most to the already complete the best or the worst, as if intensifying it — the most best, the most worst. Both forms already mark the superlative, so the extra word is unnecessary.
This is the worst headache I've had all month, not just a bad one.
This is the worst headache I've had all month, not just a bad one.
Worst needs no additional most here: that would duplicate the superlative marking.
He is the best cyclist in the regional club, better than anyone else there.
He is the best cyclist in the regional club, better than anyone else there.
Better compares him against the other club members; best summarises his position within the group.
Farthest or furthest: the scope of variation
The cited British Council material gives far two alternatives at each degree: farther/further and farthest/furthest. It does not establish a fixed everyday meaning distinction for physical distance: both alternatives are correct in that use.
This topic accepts both the farthest and the furthest wherever the physical-distance form is tested. Choosing one is an author’s stylistic choice, rather than a separate grammatical rule assessed here.
Of all the runners, Wilson reached the farthest checkpoint.
Of all the runners, Wilson reached the farthest checkpoint.
The furthest checkpoint would express the same meaning.
This is the furthest I have ever cycled in one day.
This is the furthest I have ever cycled in one day.
The farthest I have ever cycled is also acceptable here.
Using the forms in speech
These forms frequently occur when assessing something against several alternatives: recommending a restaurant, describing a better or worse experience, or comparing routes and results. Practise producing them readily, rather than only recognising them in a test.
To check understanding, identify the quality and the group: which option is best, worst or farthest among these options? You may invent facts for practice.
Honestly, this has been the best week of the whole project so far.
Honestly, this has been the best week of the whole project so far.
So far means “up to now” here, rather than a superlative of far.
My colleague gave the worst excuse I've heard this year, and I've heard a lot.
My colleague gave the worst excuse I've heard this year, and I've heard a lot.
I’ve heard a lot implicitly establishes a large comparison group.
Common mistakes
Incorrect:She is the goodest cook in the family.
Correct:She is the best cook in the family.
The standard superlative of good in this meaning is best.
Incorrect:This is the most bad decision he has made this year.
Correct:This is the worst decision he has made this year.
The most is used with longer regular adjectives, rather than bad, which has its own form, the worst.
Incorrect:It was the most best concert of the whole tour.
Correct:It was the best concert of the whole tour.
The best already marks the superlative; adding the most duplicates that marking.
Incorrect:Of the three villages, this one is the farrest from the station.
Correct:Of the three villages, this one is the farthest from the station.
The correct superlative of far is farthest or furthest, not farrest.
Incorrect:This laptop is the best than the one I had before.
Correct:This laptop is better than the one I had before.
A direct comparison with than requires comparative better.
Incorrect:This was the worstest winter I remember.
Correct:This was the worst winter I remember.
Worst is already the superlative of bad; do not add another -est.
Incorrect:This is worst coffee I have ever tasted here.
Correct:This is the worst coffee I have ever tasted here.
This superlative noun phrase requires the before worst coffee.