Berkeley's Argument Analysis

From the indubitable premise that ‘One cannot think or perceive something without thinking or perceiving it’, Berkeley goes on to draw the dubious conclusion that ‘Things cannot exist without being thought or perceived’. Berkeley’s premise is a tautology, since the claim that one cannot think of something without thinking of it is one that no rational being would want to deny. But from this tautological premise Berkeley draws a non-tautological conclusion, viz., that things depend for their existence on being thought or perceived and are nothing apart from our thinking or perceiving of them. Yet Berkeley’s argument is clearly formally fallacious, since one cannot derive a non-tautological conclusion from a tautological premise. How then does