It's an exception not because it's spelt differently, but because it's
really special
. You know already the rule as:
"take the 'nous' form of the verb (eg 'chanter' - nous
chantons) then add the endings as appropriate".
With être it is
really an irregular verb, so there is your exception:
je suis
tu es...
***
nous
sommes
We can't take anything off this nous form to make 'je
sommais, tu
sommais'.
.
So with être. the bane of the world as far as I'm concerned!, you have to learn it with the '
ét' prefix
j'étais
tu étais
il était
nous étions
vous étiez
ils étaient.
And yes, you are right that they have the same endings. It's just the
prefix (or rather, the 'stem') of the être form of the imperfect that is the exception to the rule
At the start that I said that it's an exception to the rule as the verb is an irrgular verb. This isn't completely right. 'aller' is irregular yet it DOES follow this rule, so the 'irregular verb = doesn't follow the rule' thing isn't really right.
PRESENT: nous
allons, donc...
j'
allais
tu
allais...
et ainsi de suite.
Make sense? Hehe. It's late...
chepas
.