First and second are better choices than firstly andsecondly for
two reasons:
- The
shorter versions serve the same purpose as the longer versions. Shorter is often considered
better in such cases.
- The -ly forms
get awkward when you reach bigger numbers such as seventhly andeighthly.
Recently, I saw someone complaining that all uses of enumeration are clumsy
elementary-school style, but I disagree and still use enumeration in my writing
when it seems appropriate. I believe enumeration can make arguments easier to
follow, although sometimes a bulleted list is a good choice too.