In English the mode of the
verbs are not changed. In German the mode
is changed from indicative
to conjunctive.
2)
Change of the tense
In English the tense of the
introductory verb defines the change of the
tenses in the subordinate clause. In German
the tenses are not changed (only the mode
- see 1)).
Have
a look at these examples
He says:
"I bought
a car."
Er
sagt: "Ich
kaufte mir ein Auto."
He says that he bought
a car.
Er sagt,
dass er sich ein Auto gekauft
habe."
He said: "I
bought a car."
Er sagte: "Ich
kaufte mir ein Auto."
He said that
he had bought a
car.
Er sagte,
dass er sich ein Auto gekauft
habe."
3)
The English system is stable
The English system is stable.
Persons that have English as mother tongue
do not necessarily know the rules but they
follow them. The German system is not stable.
There are too many rules and actually hardly
anyone follows them (not to speak about knowing
them). Therefore the construction with the
conditional form is widely used (even though
it is not correct in many cases).
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italian-online.de 
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