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We consider the maximal U(3) horizontal scheme as a handle on fermion massesand mixings. In particular, we attempt to explain the large top Yukawa couplingand the masses and mixing in the two heaviest generations. A simple model isconstructed by enlarging the matter content of the Standard Model with that ofa $10+\bar{10}$ pair of SU(5). The third generation particles get their masseswhen U(3) is broken to U(2). Top quark mass is naturally of order one. Bottomand tau masses are suppressed because of a hierarchy in the effective Yukawacouplings and not from the hierarchy in the Higgs doublet vacuum expectationvalues. The hierarchy is a consequence of the fact that the particle spectrumcontains an incomplete vector-like generation and can come from hierarchiesbetween scales of breaking of different grand unified groups. Hierarchies andmixings between the second and third generation are obtained by introducing asingle parameter epsilon' representing the breaking U(2) -> U(1). As aconsequence, we show that the successful (and previosuly obtained) relationsV_{cb} \approx (m_s / m_b) \approx \sqrt (m_c / m_t) easily follow from ourscheme.Comment: 23 pages, LaTe

Large top quark Yukawa coupling and horizontal symmetries