In the advanced stages of such a development, certain subtle difficulties occur which mean that advanced mathematical thinking must expunge itself of possible hidden assumptions that occur when visual ideas are verbalised. In the nineteenth century a number of flaws became apparent in Euclidean geometry and theoretical developments in algebra (such as non-commutative quaternions) were over-stretching simple beliefs in the manipulation of symbols. Research mathematics took a new direction using settheoretic definition and logical deduction. Theorems inspired by geometric perception and symbolic manipulation were reformulated to give a new axiomatic approach to mathematics that led on to greater generality.