Changes

I moved here BTW, if you are interested :)

Des vs de


There is this tricky thing in French - des and de with plural.
Almost all the French adjectives go after the noun they denote:
Un livre interessant
So, in plural they are used with plural indefinite 'des':
Des livres interessantes

But! when a noun is used with an adjective that precedes it, like:
Une belle femme
In this case the article for plural changes to 'de':
De belles femmes

Passé Composé and Imparfait

When thinking of difference between passé composé and imparfait, I usually imagine passé composé as a dot (or several dots) and imparfait as a line.

Imparfait

To build this tense you should drop the -ons ending from the present indicative nous form of the verb and add the imperfect endings:
je -ais nous -ions
tu -ais vous -iez
il -ait ils -aient

Meanings:
I. Habitual actions or states of being

Quand j'étais petit, nous allions à la plage chaque semaine.
When I was young, we used to go to the beach every week.


II. Physical and emotional descriptions: time, weather, age, feelings

Il était midi et il faisait beau.
It was noon and the weather was nice.

III. Actions or states of an unspecified duration

Je faisais la queue parce que j'avais besoin de billets.
I stood in line because I needed tickets.

IV. Background information in conjunction with the passé composé

Il était à la banque quand il l'a trouvé.
He was at the bank when he found it.

V. Wishes or suggestions

Ah ! Si j'étais riche !
Oh, if only I were rich!

Si nous sortions ce soir ?
How about going out tonight?

VI. Conditions in si clauses

S'il voulait venir, il trouverait le moyen.
If he wanted to come, he would find a way.

VII. The expressions être en train de and venir de in the past

J'étais en train de faire la vaisselle.
I was (in the process of) doing the dishes.

Il venait d'arriver.
He had just arrived.

NB! The verb être is an exception for this tense. It's not formed from nous sommes, but takes the irregular stem ét- and the same endings as others.
AND the vous form is étieZ

Passé Composé

To my mind, this tense is one of the easiest to remember:
The formula for it is:
avoir + participe passé
J'ai déjà mangé.
Il a déjà mangé.
Nous avons déjà mangé.

Être and pronominal verbs:
être + participe passé
Je suis allé.
Il est allé.
Nous sommes allés.

This tense denotes (1) an action completed in the past:

As-tu étudié ce weekend ?
Did you study this weekend?

Ils ont déjà mangé.
They have already eaten.

(2) an action repeated a number of times in the past:

Oui, j'ai mangé cinq fois hier.
Yes, I did eat five times yesterday.

Nous avons visité Paris plusieurs fois.
We've visited Paris several times.

(3) a series of actions completed in the past:

Quand je suis arrivé, j'ai vu les fleurs.
When I arrived, I saw the flowers.

Samedi, il a vu sa mère, a parlé au médicin et a trouvé un chat.
Saturday he saw his mother, talked to the doctor, and found a cat.

Être Verbs used with direct object

You may think that être verbs are always used with être (or else why would they have been called like that?) But there is a 'but'. Six of these verbs can take direct object! (It's annoying, isn't it). But to think logically, it's logical! :)
These nasty guys are:

descendre
monter
passer (BTW I haven't included this verb into the previous post)
rentrer
retourner
sortir

You will understand everything after looking through examples:

descendre
Il est descendu. - He went down(stairs).
Il a descendu l'escalier. - He went down the stairs.
Il a descendu la valise. - He took the suitcase down.

monter
Il est monté. - He went up(stairs).
Il a monté la côte. - He went up the hill.
Il a monté les livres. - He took the books up.

passer
Je suis passé devant le parc. - I went by the park.
J'ai passé la porte. - I went through the door.
J'ai passé une heure ici. - I spent an hour here.

rentrer
Je suis rentré. - I came home.
J'ai rentré les chaises. - I brought the chairs inside.

retourner
Elle est retournée en France. - She has returned to France.
Elle a retourné le livre. - She returned the book.

sortir
Elle est sortie. - She went out.
Elle a sorti la voiture - She took the car out.

So, when you see that an être verb is used with direct object, feel free to use 'avoir' instead of 'être'. Well, actually, you should do this ;)

Être Verbs

In French, compound tenses are formed with the help of auxiliary 'avoir' or 'être'. So French verbs are classified by which auxiliary verb they take (they are used with one and the same auxiliary in all the compound tenses).
Well, most of the verbs use 'avoir', and the short list of those requiring 'être' is easy to remember:

All the verbs are intransitive (can't take direct object) denoting some kind of movement.

NB! Derivatives of these verbs also use 'être'.

If you find it difficult to remember the verbs, here's a mnemonics for you (Dr and Mrs Vandertramp):
    Devenir
    Revenir
    &
    Monter
    Rester
    Sortir

    Venir
    Aller
    Naître
    Descendre
    Entrer
    Rentrer
    Tomber
    Retourner
    Arriver
    Mourir
    Partir
Though it includes some derivatives, the mnemonics is rather helpful, I think. (If you know a better one - please, share :)

And, of course, all pronominal verbs use être (+ 's' in the end (for Pl))

To check your grip on être verbs click here.