Readability V. Legibility
These principles of design are starkly different but they concepts which I must admit I mix up a lot of times.
If a document or text is legible doesn’t mean it is readable and vice versa. In common language the two concepts are used interchangeably and there lies the confusion.
Readability focuses on the information, that is extent of comprehension based on the complexity of words and sentences while legibility focuses on the way and manner information is presented.
Another area of confusion is ‘clarity’. Clarity applies to both readability and legibility. Clarity in terms of readability can be omitting needless words and punctuation, avoiding acronyms and using active voice etc. Clarity as it applies to legibility can clarity of text (Anti aliasing, Aliasing) size, typeface, contrast, text block, and spacing.