Learn Hardcore French: En été, Paul porte souvent un short bleu au lieu d’un pantalon. - In summer, Paul often wears blue shorts instead of pants.

✗ au été is incorrect, because with seasons like été the standard preposition is en, not à / au.
✗ en l’été is also incorrect; you do not keep the article here.
dans l’été is grammatically possible but unusual; it would sound like within the summer / at some point in the summer, not the normal, general in summer.

For a basic, habitual statement, En été is the natural choice.

Can we also say L’été, Paul porte souvent un short bleu…? What is the difference from En été?

Yes, you can say:

L’été, Paul porte souvent un short bleu…

It means almost the same as En été, Paul porte…: In (the) summer, Paul often wears…

Nuance:

L’été, … tends to suggest every summer / in summertime in general, a habitual situation.
En été, … also works for a general habit, and in practice the difference is very small in this sentence.

Both are correct; for a learner they are practically interchangeable here.

What tense is porte, and why is the present used to express a habit?

Porte is:

3rd person singular
Present indicative of porter

So Paul porte souvent… = Paul often wears…

In French, the present tense is used to express:

Current actions: Paul porte un short bleu aujourd’hui. – Paul is wearing blue shorts today.
Habits and general truths: Paul porte souvent un short bleu en été. – Paul often wears blue shorts in summer.

Just like English simple present (Paul often wears…), the French present naturally covers habitual actions, so no extra word like d’habitude is required.

Why is the verb porter used here instead of mettre?

Both verbs relate to clothing, but they are used differently:

porter = to wear / to carry
- Paul porte un short bleu. – Paul is wearing a blue pair of shorts.
mettre = to put on
- Paul met un short bleu. – Paul is putting on a blue pair of shorts.

In your sentence, we are talking about what Paul wears in general, not the act of putting it on at that moment, so porter is the correct verb.

You might use mettre in a different sentence such as:

En été, Paul met souvent un short bleu le matin.
Focus: the repeated action of putting it on.

Why does souvent come after porte instead of at the beginning or end of the sentence?

The most neutral position for many adverbs of frequency (like souvent) in simple tenses is:

Subject + verb + adverb

So:

Paul porte souvent un short bleu…

is the default word order.

Other possibilities:

Souvent, Paul porte un short bleu en été.
Also correct, but it emphasizes souvent (Often, Paul wears…).
Paul porte un short bleu en été, souvent.
Possible in spoken French, but it sounds more casual and less neutral.

For standard written French, Paul porte souvent… is the most typical structure.

In English we say shorts (plural). Why is it un short (singular) in French?

French borrowed the word short from English but treats it as:

a regular, countable masculine noun
normally used in the singular for one garment

So:

un short = a pair of shorts
deux shorts = two pairs of shorts

In French, many clothes that are “two-legged” in English but grammatically plural there (shorts, pants, jeans) are singular:

un short – shorts
un pantalon – pants / trousers
un jean – jeans

If you have several separate garments, you pluralize it in French too:

J’ai trois shorts. – I have three pairs of shorts.

Why is it un short bleu and not une short bleue or un short bleus?

Three separate points are involved: gender, number, and agreement.

Gender of short
- short is masculine, so the article must be un, not une.
Number (singular vs plural)
- We’re talking about one garment (one pair of shorts), so it is singular: un short, not des shorts.
Adjective agreement
- bleu is an adjective of color.
- It must agree with short in gender and number.
- short: masculine singular → bleu (masculine singular form).

So:

un short bleu = correct (masculine singular noun + masculine singular adjective)
une short bleue = wrong gender
un short bleus = noun is singular but adjective is plural → incorrect agreement

Why does bleu come after short and not before it?

In French, most descriptive adjectives (especially colors) come after the noun:

un short bleu – a blue pair of shorts
un pantalon noir – black pants
une chemise blanche – a white shirt

Only certain common adjectives (often describing beauty, age, number, goodness, size – sometimes remembered as BANGS) usually go before the noun:

un petit pantalon – a small pair of pants
une belle chemise – a beautiful shirt
trois shorts rouges – three red shorts (here trois is before; rouges is after)

Since bleu is a color adjective, it normally follows the noun: un short bleu.

Why is it un pantalon (singular) when in English we say pants or trousers (plural)?

As with un short, French treats pantalon as a singular countable noun:

un pantalon = a pair of pants / trousers
deux pantalons = two pairs of pants

So even though English uses the plural form pants/trousers for one garment, French uses the singular:

Je porte un pantalon. – I am wearing pants / I have pants on.
Il a beaucoup de pantalons. – He has many pairs of pants.

It’s just a difference in how each language treats the concept grammatically.

What exactly does au lieu d’un pantalon mean, and how is au lieu de used?

Au lieu de means instead of / in place of.

In your sentence:

au lieu d’un pantalon = instead of pants / instead of a pair of trousers

Structure of au lieu de:

au lieu de
- noun/pronoun
  - au lieu d’un pantalon – instead of pants
  - au lieu de ce short – instead of this pair of shorts
  - au lieu d’eux – instead of them
au lieu de
- infinitive verb
  - au lieu de porter un pantalon – instead of wearing pants
  - au lieu de travailler – instead of working

So your sentence literally means:
In summer, Paul often wears blue shorts instead of (wearing) pants.

Could we say au lieu de pantalon without un?

No, ✗ au lieu de pantalon is not natural in standard French.

You generally need a determiner (like un, le, ce, son) before a countable noun such as pantalon:

au lieu d’un pantalon – instead of (a pair of) pants
au lieu du pantalon – instead of the pants
au lieu de son pantalon – instead of his pants

You can omit the article only in special structures (with mass nouns, abstract nouns, or some fixed expressions), but pantalon here is a concrete, countable object, so you keep the article:

Correct: au lieu d’un pantalon
Incorrect: ✗ au lieu de pantalon

Where do au and d’un come from in au lieu d’un pantalon?

They are contractions:

au = à + le
- à le lieu → au lieu
  French always contracts à + le to au.
- Je vais au parc. – Je vais à + le parc.
d’un = de + un
- de un pantalon → d’un pantalon
  The vowel e in de is dropped before another vowel (the u of un), and we write d’un.

So, grammatically:

au lieu d’un pantalon = à le lieu de un pantalon (which only appears in the contracted, correct form).

Can we move En été to the end of the sentence?

Yes. You can say:

Paul porte souvent un short bleu en été.

This is also correct and very natural. The meaning stays the same.

Word order options:

En été, Paul porte souvent un short bleu au lieu d’un pantalon.
Paul porte souvent un short bleu au lieu d’un pantalon en été.

Both are possible. Placing En été at the beginning slightly highlights the time frame; placing it at the end is a bit more neutral or spoken-style, but both are fine.

Are there any tricky pronunciation points or liaisons in this sentence?

A few points to watch:

En été
- en has a nasal vowel [ɑ̃].
- été has two é sounds [e].
- You don’t pronounce a consonant between them; it’s not en-n-été, just [ɑ̃ ete].
porte
- Final -e is silent, and the t is also silent here: [pɔʁt] (with the French ʁ).
short
- Pronounced approximately [ʃɔʁt] in French (starting with sh, not s).
bleu
- Single vowel sound [blø], no -eu as two separate sounds.
au lieu d’un
- The words link smoothly: [oljø dœ̃] (the n in d’un is not pronounced; it nasalizes the vowel).
pantalon
- Final -n is not fully pronounced; it nasalizes the o: [pɑ̃talɔ̃].

There are no obligatory liaisons that create extra consonants between words in this particular sentence.