According to the Jewish encyclopedia:
http://www.jewishencyclopedia.com/view.jsp?artid=118&letter=I
The belief that the soul continues its existence after the dissolution of the body is a matter of philosophical or theological speculation rather than of simple faith, and is accordingly nowhere expressly taught in Holy Scripture. As long as the soul was conceived to be merely a breath ("nefesh"; "neshamah"; comp. "anima"), and inseparably connected, if not identified, with the life-blood (Gen. ix. 4, comp. iv. 11; Lev. xvii. 11; see Soul), no real substance could be ascribed to it. As soon as the spirit or breath of God ("nishmat" or "rua? ?ayyim"), which was believed to keep body and soul together, both in man and in beast (Gen. ii. 7, vi. 17, vii. 22; Job xxvii. 3), is taken away (Ps. cxlvi. 4) or returns to God (Eccl. xii. 7; Job xxxiv. 14), the soul goes down to Sheol or Hades, there to lead a shadowy existence without life and consciousness (Job xiv. 21; Ps. vi. 6 [A. V. 5], cxv. 17; Isa. xxxviii. 18; Eccl. ix. 5, 10). The belief in a continuous life of the soul, which underlies primitive Ancestor Worship and the rites of necromancy, practised also in ancient Israel (I Sam. xxviii. 13 et seq.; Isa. viii. 19; see Necromancy), was discouraged and suppressed by prophet and lawgiver as antagonistic to the belief in Yhwh, the God of life, the Ruler of heaven and earth, whose reign was not extended over Sheol until post-exilic times (Ps. xvi. 10, xlix. 16, cxxxix. 8).
As a matter of fact, eternal life was ascribed exclusively to God and to celestial beings who "eat of the tree of life and live forever" (Gen. iii. 22, Hebr.), whereas man by being driven out of the Garden of Eden was deprived of the opportunity of eating the food of immortality (see Roscher, "Lexikon der Griechischen und Römischen Mythologie," s.v. "Ambrosia"). It is the Psalmist's implicit faith in God's omnipotence and omnipresence that leads him to the hope of immortality (Ps. xvi. 11, xvii. 15, xlix. 16, lxxiii. 24 et seq., cxvi. 6-9); whereas Job (xiv. 13 et seq., xix. 26) betrays only a desire for, not a real faith in, a life after death. Ben Sira (xiv. 12, xvii. 27 et seq., xxi. 10, xxviii. 21) still clings to the belief in Sheol as the destination of man. It was only in connection with the Messianic hope that, under the influence of Persian ideas, the belief in resurrection lent to the disembodied soul a continuous existence (Isa. xxv. 6-8; Dan. xii. 2; see Eschatology; Resurrection).
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