_Zodanig_ and _dusdanig_ are formal forms of [zo'n and zulke](#/lesson/Pronouns.De09).
They mean 'such' as in 'of such a nature' or 'of such a degree'. The two mean practically the same.
We use them in cause-and-effect sentences:
formal | Ze hadden zodanige fouten gemaakt, dat het project moest worden afgelast. | The mistakes they had made were such that they had to cancel the project.
Ze hadden dusdanige fouten gemaakt, dat het project moest worden afgelast. | |
common | Ze hadden zulke fouten gemaakt, dat het project moest worden afgelast. | They had made such mistakes, that they had to cancel the project.
As you can see, _zodanig_ and _dusdanig_ are used interchangeably. If you want to know the exact distinction: We use _zodanig_ more often when we talk about 'of such nature' and _dusdanig_ in the sense of 'of such a degree'.
Whether they get -e at the end depends on the word they precede. Before _de_-nouns, we add -e at the end. In this respect, they behave like [adjectives](#/lesson/AdverbsAndAdjectives.01).
Zodanig/dusdanig and 'zo' (so)
In the example above, _zodanig/dusdanig_ precedes a noun and thus behaves as an adjective. It can also say something about a verb or adjective, which makes it an [adverb](#/lesson/AdverbsAndAdjectives.01).
In this case, we often use (exclamative) _zo_.
formal | Ze hadden het dusdanig naar hun zin, dat ze besloten langer te blijven. | They were enjoying themselves to such a degree, that they decided to stay longer.
common | Ze hadden het zo naar hun zin, dat ze besloten langer te blijven. | They were enjoying themselves so much, that they decided to stay longer.
An adverb never receives an extra -e at the end
As you can see, _zo_ is the common form.
formal | De kinderen waren dusdanig moe, dat ze meteen in slaap vielen. | The children were tired to such a degree that they fell asleep immediately.
common | De kinderen waren zo moe, dat ze meteen in slaap vielen. | The children were so tired that they fell asleep immediately.