Sentence:  It need be no concern of his how we come, through the joint action of our double nature, to apprehend at first those truths which, when apprehended, he knows to be necessary. The metaphysician has only to <WSD>constate</WSD> such facts ; it is the business of the psychologist to explain them. 
Meaning of the word marked with <WSD> tags:  To ascertain; to verify; to establish; to prove.