In, Out, Front, Back

I do not know why but I struggled for a long time to come to terms with some very basic yet important nouns and prepositions in French. I refer to the English equivalents of in, inside, out, outside, front, back and similar.

Let us start by looking at NOUNS:

l'avant          THE front
l'arrière        THE back

"L'avant" does NOT mean "in front" or "in front of". It means "THE front", a noun. I know I am getting carried away with all the caps but I had to emphasise these kinds of things to avoid confusion for myself when trying to master these words.

Let us now change these nouns into prepositions. In English, we would say "in front of" and "behind". Notice how in English we sometimes use the word "of" to create a preposition from a noun. This is the same in French: we use "de".

Thus, we have de + avant = devant and de + arrière = derrière.

Examples

Il est à l'avant de l'avion.          He is in/at the front of the plane.[Perhaps he is in Business Class.]
Il est à l'arrière de l'avion.        He is in/at the back of the plane. [He is in Economy Class.]
Il est devant l'avion.                 He is in front of the plane. [That could be dangerous.]
Il est derrière l'avion.               He is behind the plane. [Perhaps he is following the plane in a
                                               fighter jet.]


Let us know turn to inside and outside. Again, we will start with the nouns:

l'intérieur          THE interior, THE inside
l'extérieur         THE exterior, THE outside

To convert these into prepositions, we do use "de" but we attach "de" to synonyms rather than the words above. The prepositions are:

dedans          inside
en dehors      outside

Examples

Il est à l'intérieur de la maison.          He is inside the house.
Il est à l'intérieur/dedans.                   He is inside.
Il est à l'extérieur de la maison.         He is outside the house.
Il est à l'extérieur/en dehors.              He is outside.

Notice how we can use à l'intérieur and à l'extérieur instead of dedans and en dehors respectively. However, we cannot use dedans or en dehors in place of à l'intérieur or à l'extérieur. So, for example, it would be wrong to say:

Il est dedans la maison.
Il est en dehors la maison.