The Voynich Manuscript is a cipher because...?

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It can be difficult to separate a cipher from a constructed language.

Maybe a better question would be, why is the Voynich Manuscript not a natural language?


In any case, it's worth listing the features of the text that are suggestive of a cipher.

Here are some that i've seen, in no particular order:

Characters 'p' and 'f' are more likely to occur in a line already containing 'p' or 'f'.
In some cases this results in fairly evident You are not allowed to view links. Register or Login to view.. This feature is compatible with a cipher which operates on individual lines.


The character entropy is relatively low.
Low entropy is compatible with a verbose cipher.

The word variability is high.
For an example see You are not allowed to view links. Register or Login to view.. High word variability is compatible with a cipher which employs null characters. It's also compatible with a code-book cipher, but that seems less likely.

There are few repeated word sequences.
Also compatible with a dynamic cipher which operates on individual lines.

In some of these cases, a fairly sophisticated cipher would need to be employed, which is improbable at the time the VM was created.

However it's worth mentioning that the usage of null characters can transform a simple substitution cipher into something that's extremely difficult to break.