Italic is another style of letter, akin to Roman, but with a more humanist nature.
Italic is not the opposite of Roman, though. It is the opposite of Oblique. Oblique styles may also be called Sloped Roman, and they are mostly the same letterforms found in a Roman face, with a mechanical slant applied (See Oblique). “True” Italic letterforms have been drawn so that they are more formally differentiated from upright Roman letters, the inclination or “cursiveness” (Cursive) is natural to Italics, as it has been conserved from its origins (See Aldus Manutius).
Also some formal aspects such as the particular glyphs used to represent letters are characteristic of Italics. The lowercase “a” for instance, is not the humanist lowercase “a” (As in Helvetica), but the much more rounded “a” similiar to the one seen in Avant Garde for example. Another character that makes Italics easy to distinguish is the lowercase “f” which extends below the baseline.
Both Oblique and Italic are used for similar proposes within texts, sometimes for emphasizing or to make a citation evident, even though whole texts can be writing in Obliques or Italics. Fonts may include Obliques or Italics, Adrian Frutiger’s Frutiger uses obliques but Frutiger Next has Italics, for example.
In the last years more and more attention is being put unto this difference, and fonts with Italics are gaining value for their aesthetic gain (seen as positive diversity).
The new Sans bundled with Windows Vista for example, have all specially designed Italics.
dot-font: Slanted Communication