"et" is a coordinating conjunction that links two elements. "est" is the verb être conjugated in the present tense. To tell them apart, replace the word with "était": if the sentence still works, it is "est". If it does not, it is "et".
Replace with "était". If it works, write "est". If not, write "et".
Examples
Il est grand et mince.
Key word(s): est, et
"Il était grand" works (the verb). "Grand était mince" does not work (the conjunction).
Elle est contente.
Key word(s): est
"Elle était contente" works.
Un chat et un chien.
Key word(s): et
"Un chat était un chien" does not work, so this is the conjunction.
Le ciel est bleu et dégagé.
Key word(s): est, et
"Le ciel était bleu" (verb) + "bleu et dégagé" (conjunction).
Pierre et Marie sont amis.
Key word(s): et
"Pierre était Marie" does not work.
Common mistakes
Mixing up the two when they appear one after the other ("il est grand et fort").
Writing "il et grand" (using the conjunction instead of the verb).
Writing "Pierre est Marie" (using the verb instead of the conjunction).
Test yourself
Le soleil ___ chaud.
"Le soleil était chaud" works.
Pommes ___ poires.
"Pommes était poires" does not work.
Il ___ fatigué ___ il dort.
"Il était fatigué" (verb) + "et il dort" (conjunction).
Tips to remember
"et" can always be replaced by "et puis" or "ainsi que".
"est" can always be replaced by "était" or "sera".
In a list, it is always "et": "rouge, bleu et vert".
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