It is unfair and unreasonable, however, to assert that the sedevacantist — who merely puts two entirely defensible propositions together and draws a logical conclusion from them — has “rejected the authority of the Pope.” Such is tantamount to calling the sedevacantist a schismatic. But he is no such thing, as is evident from one highly respected commentary on the Code:
“Finally, one cannot consider as schismatics those who 1)refuse to obey the Roman Pontiff because they would hold his person suspect or, 2)because of widespread rumors, 3)doubtfully elected (as happened after the election of Urban VI), or 4)who would resist him as a civil authority and not as pastor of the Church.” (Wernz-Vidal, Ius Canonicum [Rome: Gregorian 1937], 7:398, my emphasis.)
(Excerpt from Fr. Cekada's article "Have I rejected the Pope?")