Capital letters are also known as caps, capitals, upper case, large letters or majuscule. They are a part of Roman alphabet but seem to have may issues when being used frequently or instead of lowercase letters.
Troubles reading capitals
The word is out there that they cause troubles reading. The theory on reading says we read not by recognizing each letter but by recognizing word shapes. When words are written in lowercase letters, they have different shapes due to different sizes of the letters (ascenders, descenders), but when we write in capital letters, we always get the shape of the block which makes shape recognition harder.
Some people say that we are just used to reading lowercase letters and that we would have no trouble reading upper case if we were used to reading them so frequently. Well, I agree that we’d have no trouble reading those letters since we wouldn’t be focused on recognizing word shapes but rather on recognizing distinctive strokes inside a ‘block’ of a word. But upper case letters are larger/ taller than lowercase and undoubtedly it takes more time to read them. Also, lowercase developed from pen writing so these shapes are more fluent, round and simpler and while looking from type design perspective, upper case letters have poorly solved interspaces and complex forms.
Words written in capital letters are understood as something important or something we should pay attention to. Or somethimes they have negative conotations when taken for screaming or shouting.
What about using caps in web design?
It’s harder to properly space and control spacing of uppercase letters in web design. If not done properly, we get awkward white spaces that destruct the coherency of words and text. If using caps is the style of your website you are keen on, then use it freely. Using caps in paragraphs will ruin its homogenized appearance so if possible, use small caps. Headings are much more readable in lowercase, but if there’s only a few words to be used in uppercase, it will work fine. Large boxes of text with uppercase letters should be avoided as these are too hard to read. Using uppercase in CTAs is ok since it will bring more attention to it. Some fonts work better than the others with uppercase letters, it is entirely up to the designer to decide how to use it to get proper reaction and engagement from users.