Sentence:  But it is not feigned on a "tabula rasa", as if at random: rather, the declaration of immediate intention appears to be formed in the way a "decision" is formed, "constrained" by the (pretended) "fact” that there is the sound of footsteps from the basement, the (<WSD>"un"pretended</WSD>) fact that such a sound would now be unlikely if therre weren't an intruder in the basement, the (<WSD>"un"pretended</WSD>) awfulness of there being an intruder in the basement, and so forth. 
Meaning of the word marked with <WSD> tags:  Based in fact; genuine; actual.