  Alignments of spiral galaxies were thought to result from tidal torquing,
where tidal field of the cosmic large-scale structure exert torquing moments
onto dark matter haloes, determining their angular momentum and ultimately the
orientation of galactic discs. In this model, resulting intrinsic ellipticity
correlations are typically present on small scales, but neither observations
nor simulations have found empirical evidence; instead, simulations point at
the possibility that alignments of disc galaxies follow a similar alignment
model as elliptical galaxies, but with a weaker alignment amplitude. In our
article we make the case for the theory of linear alignments resulting from
tidal distortions of the galactic disc, investigate the physical properties of
this model and derive the resulting angular ellipticity spectra, as they would
appear as a contribution to weak gravitational lensing in surveys such as
Euclid's. We discuss in detail on the statistical and physical properties of
tidally induced alignments in disc galaxies, as they are relevant for
mitigation of alignment contamination in weak lensing data, comment on the
consistency between the alignment amplitude in spiral and elliptical galaxies
and finally, estimate their observability with an Euclid-like survey.
