Knowledge is the intellectual manipulation of carefully verified observations.

The facts which have caused us to believe in the dominance of the pleasure principle in mental life also find expression in the hypothesis that the mental apparatus endeavours to keep the quantity of excitation present in it as low as possible or at least to keep it constant.

One thing only do I know for certain and that is that man's judgments of value follow directly his wishes for happiness-that, accordingly, they are an attempt to support his illusions with arguments. [p.111]

Neither in my private life nor in my writings, have I ever made a secret of being an out-and-out unbeliever.

If youth knew; if age could.

Just as a satisfaction of instinct spells happiness for us, so severe suffering is caused us if the external world lets us starve, if it refuses to sate our needs. One may therefore hope to be freed from a part of one's sufferings by influencing the instinctual impulses.

The most complicated achievements of thought are possible without the assistance of consciousness.