Re: Ijtehad..
Ijtihad is applied when the answer to an issue is not found directly in the Quran, it is not found directly in the Sunnah, it cannot be found by analogy to something in the Quran or Sunnah, and when the ulema are not united in their opinion on the topic (in that order of precedence).
Ijtihad is the last resort option in Islamic jurisprudence, applied when all other sources cannot resolve an issue. It has been applied more and more since the start of the previous century.