Italic vs oblique
An italic redraws letters with cursive forms; an oblique mostly tilts the upright design. Check the 'a' and 'g' to spot the difference.
See it
What it is
A true italic is a separately drawn companion to the roman, often with cursive construction: a single-storey 'a', a looped or simplified 'g', new joins, and adjusted spacing. An oblique keeps the roman letterforms and slopes them. The distinction is old: Francesco Griffo cut the first italic for Aldus Manutius in Venice in 1501, based on the chancery hand, and it was a separate alphabet from the start. Faces such as Helvetica traditionally use obliques, and Helvetica Oblique is honestly named where many families would have written Italic; Garamond has unmistakably redrawn italics.
Use the real italic when emphasis should add a second voice, especially in books, essays, and editorial work. Use an oblique when the family is deliberately rational and the sloped roman is part of its design, or when labels need emphasis without a change of construction.
Gotcha: font menus and CSS naming are not reliable taxonomies. A font file may be marketed as Italic even when its drawing is oblique, and 'font-style: italic' can trigger browser synthesis if no italic face was loaded. Inspect the 'a', 'f', and 'g', and disable synthesis before judging what the family actually contains.
Ask AI for it
Build a three-column HTML specimen for roman, true italic, and oblique. Set the roman and true-italic columns in the system font with 'font-family: Georgia, serif', switching the second column with 'font-style: italic', since Georgia ships a drawn italic. For the oblique column use 'font-family: Helvetica, Arial, sans-serif' with 'font-style: oblique 12deg', so the roman is slanted rather than swapped for cursive forms. Apply 'font-synthesis: none' to the true-italic column only, so a missing italic fails visibly. Use the string 'a g f minimum' at 96px and label every glyph that changes construction, not merely angle.