The general rule is to put the adjectives after the noon, however you noticed that in French they can also be before it; sometimes it is not important, usually when an adjective is before the noun, it is acceptable to have it sometimes after, for example:
– Un grand livre or un livre grand (even if un grand livre sounds better with the adjective grand before), but we are going to see that, in some cases, it is not possible (this example with Grand does not work with people see below).
Here is the video:
4 categories, adjectives about: age, size, beauty, bad and good. We can call it the BAGS (for Beauty, Age, Goodness, Size)
A- Age: old, young
-Un vieux livre
-Une vieille voiture
-Un jeune garçon
-Une jeune fille
B- Size: small, little, big, tall…
-Un grand livre
-Une grande voiture
-Une petite maison
C- Beauty: Good-looking, handsome…
-Un beau livre
-Un bel homme (ou un homme beau)
-Une belle fille
-De beaux livres
D- Bad, Good: mauvais, méchant, bon…
-Un bon garçon (a good boy)
-Une bonne élève ( a good pupil)
-De mauvais garçons (bad boys)
-“Un plat épicé” is a spicy dish, but you cannot say “un épicé plat”, it is not correct in French.
-“Un grand ami” is a great friend but “un ami grand” is a tall friend.
-“Un viel ami” is a friend you have been knowing for years but “un ami vieux” is a friend who is old.
-“Un petit ami” is a boyfriend and “un ami petit” is a little friend.
Un cher ami: a dear friend but une voiture chère is an expensive car.
Une histoire drôle is a funny story but une drôle d’histoire is a weird story
Un homme grand is a tall man but un grand homme is a famous man
Mon propre libre is my own book but un livre propre is a clean book
Un seul chien is one dog only but un chien seul is a dog alone