We use a superlative to say that a thing or person is the most of a group. When we use a superlative adjective ('the tallest student') before the noun, we generally use it with 'the'. This is because there's only one (or one group) of the thing we are talking about. There is one student who is the tallest in the class, and because it's clear to the listener which one we mean, we usually use 'the':

• She's the most beautiful girl I've ever seen.
• It's the best café in London.
• John and Lisa are the most intelligent students here.
• This bowl is the biggest one.
• 
  
  
  
  

Remember, we don't use 'the' when there is a possessive:

• He's my best student.
• That's our most important goal.

It's possible to drop 'the' when the adjective is used later in the sentence, rather than directly before the noun. We can choose either 'the' or 'no article', with no change in meaning:

• She is (the) most beautiful.
• This café is (the) best.
• John and Lisa are (the) most intelligent.
• This bowl is (the) biggest.

This is not possible when the adjective comes directly before the noun:

• He is fastest swimmer.
• 
  

Try an exercise about superlatives with 'the' here.

With superlative adverbs, we can also choose to use 'the' or 'no article'.

• Luke reads (the) fastest.
• I like vanilla ice cream (the) best.
• She can speak six languages, but she speaks Spanish (the) most confidently.

These examples all compare one person or thing with other people or things. However, sometimes we compare a person or thing in one situation with the same person or thing in a different situation. In this case, when the superlative adjective or adverb is later in the sentence, we usually don't use 'the'. Compare these two sentences:

• I'm most productive early in the morning [I'm more productive in the morning than I am in the afternoon or the evening].
• I'm the most productive early in the morning [I'm more productive than the other people in my office first thing in the morning].
• 
  
  
  
  

More examples:

• Julie does swimming, running and cycling. She's always most tired after cycling.
• John types most quickly when he's drunk a lot of coffee!
• Tea is˜ best when you drink it very hot.
• London is most depressing in January.

Try another exercise about using 'the' with superlatives here.

(This is an extract from my book: A and The Explained) 

Notes:

1. The written lesson is below.
2. Links to quizzes, tests, etc. are to the left.

There are two types of superlative: relative and absolute.

Relative: John is the smartest boy in the class.

Absolute: John is very smart.

The relative superlative describes a noun within the context of some larger group.

John is the smartest boy in the class.

Mary is the youngest person in the room.

Of the three, Moe is the meanest.

The absolute superlative does not describe the noun in the context of a larger group.

John is very smart.

The book is extremely expensive.

The food is indescribably tasty.

In English, the relative superlative is formed by using the word “most” or the ending “-est.”

John is the most intelligent boy in the class.

Mary is the smartest girl in the class.

In Spanish, the relative superlative construction is similar to the comparative.

definite article + noun + más (menos) + adjective + de

Here are some superlative examples.

Juan es el chico más inteligente de la clase.

John is the smartest boy in the class.

Bill Gates es el hombre más rico de los EEUU.

Bill Gates is the richest man in the U.S.

Just like in English, the noun can be omitted. All of the following are correct.

María es la chica más delgada de la clase.

Mary is the thinnest girl in the class.

María es la más delgada de la clase.

Mary is the thinnest in the class.

The absolute superlative for adjectives has three possible forms.

muy + adjective

sumamente + adjective

adjective + ísimo (-a, -os, -as)

The following translations are somewhat arbitrary. Each superlative statement is a little stronger than the one that precedes it.

muy guapo

very handsome

sumamente guapo

extremely handsome

guapísimo

indescribably handsome