كَالْأَحْوَلِ يَرَى الْوَاحِدَ اثْنَيْنِ
As when someone sees one thing as two.
The example presents a single external object but a doubled visual appearance under an abnormal condition. “It appears double to me” reports an experience; “there are actually two objects outside” makes an additional claim about reality. The two are not equivalent.
The external claim can be tested by changing the viewpoint, checking the object by other suitable means, or using corroborating evidence. Identifying the cause of an illusion makes correction intelligible.
The example therefore supports careful evaluation of perception; it does not establish that every external judgment based on the senses must be false.