The TULIP was constructed in response Arminianism, which asserts free will across the spectrum of salvation.
The acronym is as follows:
Total Depravity (also known as Total Inability and Original Sin)
Limited Atonement (also known as Particular Atonement)
Perseverance of the Saints (also known as Once Saved Always Saved)
According to the Calvinist Corner,
The doctrine of Total Depravity is derived from scriptures that reveal human character: Man’s heart is evil (Mark 7:21-23) and sick Jer. 17:9). Man is a slave of sin (Rom. 6:20). He does not seek for God (Rom. 3:10-12). He cannot understand spiritual things (1 Cor. 2:14). He is at enmity with God (Eph. 2:15). And, is by nature a child of wrath (Eph. 2:3). The Calvinist asks the question, "In light of the scriptures that declare man’s true nature as being utterly lost and incapable, how is it possible for anyone to choose or desire God?" The answer is, "He cannot. Therefore God must predestine."
Calvinism also maintains that because of our fallen nature we are born again not by our own will but God’s will (John 1:12-13); God grants that we believe (Phil. 1:29); faith is the work of God (John 6:28-29); God appoints people to believe (Acts 13:48); and God predestines (Eph. 1:1-11; Rom. 8:29; 9:9-23).
Well, that's all-n-good, but like so many other doctrines of men, we pick-n-choose which verses support our perfect ideal and promote those scriptures, all the while ignoring the others that cast doubt or contradiction upon our position.
What has happened here is a failure to consider the whole counsel of God. In other words, we should also consider other scripture before making this leap of blind faith. I, therefore, submit the one scripture they have not provided, the single context which plucks the 'T' from its root, and unravels the doctrine of Total Depravity.
Acts 17:22-28 (emphasis mine)
So Paul stood in the midst of the Areopagus and said, “Men of Athens, I observe that you are very religious in all respects. For while I was passing through and examining the objects of your worship, I also found an altar with this inscription, ‘TO AN UNKNOWN GOD.’ Therefore what you worship in ignorance, this I proclaim to you. The God who made the world and all things in it, since He is Lord of heaven and earth, does not dwell in temples made with hands; nor is He served by human hands, as though He needed anything, since He Himself gives to all people life and breath and all things; and He made from one man every nation of mankind to live on all the face of the earth, having determined their appointed times and the boundaries of their habitation, that they would seek God, if perhaps they might grope for Him and find Him, though He is not far from each one of us; for in Him we live and move and exist, as even some of your own poets have said, ‘For we also are His children.’