Apostrophe (prounounced “aPOStrufee”) misuse is very common among native speakers, thus setting a bad example for learners of English.
An apostrophe followed by an s can be one of three things, according to context:
1. contraction of ‘is’ e.g. “Jane’s a pain in the neck” (Jane est un casse-pied)
2. Contraction of ‘has’ e.g. “Jane’s been getting on my nerves all day” (Jane m’enerve toute la journée)
3. Indication of possession. “This is Jane’s stupid brother” (c’est le frère stupide de Jane)
Plurals do not take an apostrophe:
A pair of Jeans (NOT Jean’s)
An apostrophe followed by a d can be either ‘had’ or ‘would’. When used as an auxiliary verb, had is always followed by the past participle, as in the past perfect. Would is always followed by an inifinitive, and is usually (but not always) a conditional.
Do this little exercise to practise the difference between would and had.