"The baby and the bottle."
Translation:An leanabh agus am botal.
No difference in meaning. 'Am' is used before certain consonants - b,f,p,m. (Same as in English: imperfect rather than inperfect, immaterial rather than inmaterial, imbibe rather than inbibe. This correlation does not seem to extend to 'f' though - we say inflate not imflate.)
Well there are two situations that have to be considered separately. One is where there could, at least in principle, be lenition, and the other is where there couldn't.
Nothing on this page applies where there is any hint of lenition (so a' bhean 'the wife') but otherwise I think the rule about bfpm is pretty reliable.
Even when we discover later that an can also mean 'their', the rule still works.