it have

Hello,

I read the following sentence...

"Since all senses are nothing but forms of perception of the soul: assume only that it have distinct perception and hence distinguishing marks–with the distinguishing marks it does have inner language". (On the origin of language; translated out of German into English by Alezander Gode)

...and thought:

Shouldn't the first ''have" in this sentence not be "has"?

And with the verb "assume" is the writer telling me to just "adopt the idea" that the soul has (have) distinct perception and hence distinguishing marks–with the distinguishing marks it does have inner language?

With kind regards,
Den Atzeni
from the Netherlands