יָסַף occurs almost two hundred times, mostly in the Qal and Hiphil (six times in the Niphal). The LXX translates usually with προστίθεμαι. No cognate is found in Ugaritic.
A very common usage of ‏יָסַף is “to do again,” as in Gen 4:2, “And again, she gave birth to his brother Abel” (cf. 38:5). In the case of Abraham taking Keturah as wife, 25:1 states, “Now Abraham had taken another [lit. added or took again a] wife.” Sometimes, especially with a negative particle, it is translated “no more” as in the moving scene where Judah quotes Joseph, “Unless your youngest brother comes down with you, you shall see my face no more” (lit. you shall not add to; see 44:23).
The literal idea “to add” is clearly evident in Lev 27:13, 15, 19, 27 where repeatedly Moses writes about the person who makes a vow that “he shall add a fifth of the value” if he should wish to redeem an object or property. The case of Hezekiah also is to the point, where in response to his prayer, the Lord promises, “I will add fifteen years to your life” (Isa 38:5). Rachel, in naming her firstborn Joseph, prays, “May the Lord give me [lit. add to me] another son.” Both Isaiah and Rachel acknowledge that longevity and progeny are at the sovereign discretion of God. In this connection observe Prov 10:27, “The fear of the Lord prolongeth days.” See also 9:11.
There is a negative note in connection with יָסַף. This is the human ethical problem of sin. It is first encountered with Pharaoh, “But when Pharaoh saw that the rain and the hail and thunder had ceased, he sinned again (lit. he added to sin) and hardened his heart” (Ex 9:34). But this is the case even with the people of God, as the recurring phrase in Judges “and the children of Israel did evil again (lit. added to do evil) in the sight of the Lord” (3:12; 10:6; etc.). This heaping up of something need not be totally negative. Ps 71:14 quotes the psalmist as saying, “I will increase thy praise” or as KJV “and will yet praise thee more and more.”