[LyndsySimon]

The morning-after pill has two methods of action, IIRC - preventing ovulation, and making the womb inhospitable for implantation. In the latter case conception occurs.

[Domenic_S]

We're wandering from the topic, but I don't believe that's correct. From https://en.wikipedia.org/wiki/Levonorgestrel#Emergency_birth... -

The primary mechanism of action of levonorgestrel as a progestogen-only emergency contraceptive pill is, according to International Federation of Gynecology and Obstetrics (FIGO), to prevent fertilization by inhibition of ovulation and thickening of the mucosa of cervix. FIGO has stated that: "review of the evidence suggests that LNG [levonorgestreol] ECPs cannot prevent implantation of a fertilized egg.

(references on the wiki page as always)

[LyndsySimon]

They've removed the notice from that specific type of ECP (and I was not aware of that), but it's still present on other types, including some that are common in the US: https://en.wikipedia.org/wiki/Emergency_contraception#Mechan...

[Falling3]

Conception =/= Fertilization. The latter case you mentioned involves fertilization, not conception.

[LyndsySimon]

Your definition differs from every popular and academic source I've ever found.

Example: http://www.thefreedictionary.com/conception

"Formation of a viable zygote by the union of the male sperm and female ovum; fertilization."

[Falling3]

Farther down on that same page: "the fertilization of an ovum by a sperm in the Fallopian tube followed by implantation in the womb"