Tilenus holds this immortality natural rather than supernatural, yet by God's covenant, not the body's own power
The Reformed, however, maintain that the immortality man had in his first integrity should be called natural rather than supernatural, and that the first man really was in some sense immortal by nature. This is what Tilenus teaches in the eighth thesis of the disputation just cited, where he says that man is truly called immortal by nature.
Yet in the second thesis, explaining his meaning more precisely, he teaches that the first man's body was in itself corruptible, since it was made up of contrary qualities in conflict with one another, but that by God's covenant it would have been incorruptible had man continued in obedience to God without sin.
Latin
XXIII. Caeterum istam immortalitatem quae homini in integritate primigenia competebat, pertendunt dici debere potius naturalem quam supernaturalem, & revera primum hominem aliquo sensu fuisse natura immortalem. Haec est doctrina Tileni Disputationis modo citatae Thesi octava. Ubi asserit hominem vere dici natura immortalem. Thesi tamen secunda mentem suam distinctius explicans, docet corpus primi hominis per se quidem fuisse corruptibile, quippe ex contrariis, & inter se pugnantibus qualitatibus conflatum: Veruntamen ex Dei pacto incorruptibile fuisse futurum, si homo in Dei obsequio constitisset sine peccato.