What is the difference between the possessive adjective
suus (his, hers, its, theirs)
(and its declensions)
and the genitive, possessive pronoun
eius (of her, of him, of it)?
Can these words be used interchangeably?
All forms of se, including suus, normally refer to the subject of the main clause of the sentence. Eius, however, normally does not refer to this subject, but to someone else. So the two words have different meanings.
Sextus Tarquinius crudelis est. Lucretia praevidet mortem suam.
"S.T. is cruel. Lucretia foresees her own death."
Sextus Tarquinius crudelis est. Lucretia praevidet mortem eius.
"S.T. is cruel. Lucretia foresees his death."
The words suam and eius must be interpreted this way in the examples above; suam cannot refer to Tarquinius, nor can eius refer to Lucretia.