[…] this assumption is itself subjected to criticism, resulting in a suggestion that what the "semantic differential" measures is not the "meaning", but chiefly the affect, or the "emotive influence", of words.
- Weinreich (1958), a pag.347

They would have capitalized on the excellent reliability of the evaluative factor (as a measure of affect or attitude) in contrast with the relatively poor performance of all other factors, which seem to have progressively less and less to do with affect, i.e. with what the semantic differential measures.
- Weinreich (1958), a pag.360

What the semantic differential IS equipped to measure seems to be some aspect of the affect of words, their so-called "emotive influence", their power to produce extralinguistic emotional reactions.
- Weinreich (1958), a pag.359