In his 40 theses for the Heidelberg disputation, also of 1518, Luther says of man's powers in spiritual matters: "13. Free will after sin [the Fall] is a mere titular affair [an empty title only], and sins mortally when it does what it is able to do. _Liberum arbitrium post peccatum res est de solo titulo et dum facit, quod in se est, peccat mortaliter._" "16. A man desirous of obtaining grace by doing what he is able to do adds sin to sin, becoming doubly guilty. _Homo putans, se ad gratiam velle pervenire faciendo, quod est in se, peccatum addit peccato, ut duplo reus fiat._" "18. It is certain that a man must utterly despair of himself in order to become apt to acquire the grace of Christ. _Certum est, hominem de se penitus oportere desperare, ut aptus fiat ad consequendam gratiam Christi._" (W. 1, 354.) By way of explanation Luther added to thesis 13: "The first part [of this thesis, that free will is a mere empty title] is apparent, because the will is a captive and a servant to sin, not that it is nothing, but that it is free only to [do] evil--_non quod sit nihil, sed quod non sit liberum nisi ad malum._ John 8, 34. 36: 'Whosoever committeth sin is the servant of sin. If the Son shall make you free, ye shall be free indeed.' Hence, St. Augustine says in his book _De Spiritu et Litera:_ Free will without grace can only sin--_non nisi ad peccandum valet._ And in his second book against Julianus: You call that a free will which in truth is captive, etc." To thesis 16 Luther added: "When man does what he is able to do (_dum facit, quod est in se_), he sins, seeking altogether his own. And if he is minded to become worthy of, and apt for, grace by a sin, he adds proud presumption."