The following shows the main verb in bold, and helps demonstrate the meaning of the sentence through added punctuation and rewording.

Add punctuation:

>Whatever I have (up till now) accepted as, "most true and assured",  
I **have gotten** either from the senses or through the senses.

Rearrange and reword:

>Until now, all the things that I have accepted as reality,  
I **have gotten** either from the senses or through the senses.

Simplify language:

>Until now, what I considered to be true and real  
**was based** on the senses--either directly or indirectly.