Both longitudinal deceleration (Komissarov 1988) and transverse velocity shear in a boundary layer (Laing 1992, 1994) are essential ingredients of Laing's explanation for the sidedness and polarization evolution at the bases of FR I jets. The effects of relativistic Doppler boosting/hiding on intensity (Komissarov 1988, 1990) apparently combine with those of aberration on polarimetry in the right way to relate the apparent magnetic field directions and jet sidedness much as observed (Laing, these Proceedings).
The Green Bank meeting debated how to weigh symmetry constraints on the speeds of FR I jets on multi-kiloparsec scales (O'Dea 1985) against the similarities in sidedness and magnetic field configuration (e.g., Bridle 1982) between their bases and entire FR II jets. Many ingredients of the decelerating-jet model were available in 1984: the ``spine'' field configuration (Laing 1981), the surface shear layer (Baan 1980), the deceleration and recollimation mechanism for low-Mach-number jets (Phinney 1983), and evidence for superluminal motion at the base of an FR I jet (3C120-Walker et al. 1982; Walker 1984). But the path to the model had still to be cleared by imaging of complete samples of FR I jets on both parsec and kiloparsec scales, and by using the depolarization asymmetry as a primary orientation guide. The model now unites so many distinct correlations for FR I jets that its essentials must surely be correct, even if key details are not yet in place: e.g., the boundary-layer field structures and depths, the magnitude and origin of the mass influx. (Is the mass is added mainly by turbulent entrainment (Bicknell 1984, 1986, 1995, and these Proceedings; De Young, these Proceedings) or by winds from stars within the jets (Komissarov 1994)?) If the strong-deceleration region of many FR I sources is indeed accessible to our work-horse instruments, we may be able to constrain jet velocity fields and mass influxes in the regime where the FR I vs. FR II character of large-scale sources is settled. These constraints should help to establish dynamical models for the FR I/II division in the radio-optical luminosity plane (Owen & Ledlow 1994), as proposed here by Bicknell (these Proceedings). It will also be important to see if the field ordering required by the observed polarization near the boundaries of FR I jets is compatible with the large-scale ``gulping'' (De Young, these Proceedings) needed to decelerate them rapidly by entrainment. Where is the entrainment region (if any) relative to the observed jet?