Hi all. Since some people were asking about denominational differences, I wanted to give an insiders perspective, since a dictionary or encyclopedia definition of an Orthodox or Conservative Jew isn't necessarily going to represent the complex range of observance. My own identification is typically complex: I grew up going to an Orthodox synagogue, and still sometimes go to Orthodox services; my practice and belief probably puts me closest to the more traditional end of the Conservative movement, but I've never actually been a member of a synagogue affiliated with the movement - like many active Jews of the younger generation, I've gravitated toward smaller, independent "minyanim" (prayer groups) that might look more or less like a typical Conservative service, but that avoids institutional labels. That may be one explanation for why the victims were all older; the 50 + contingent are those that may be most likely to still be members of the more traditional, big congregation.
Theologically, the main difference between the Orthodox and Conservative movements involves the status of the oral law. Both movements, in theory, believe that the Torah (Bible) comes from G-d and that we are obligated to follow His commandments. The Orthodox movement, however, gives a similarly elevated status to that Talmud, or oral law: essentially, a tradition passed down by successive generations of rabbis. Because of the belief that the rabbis of the earlier generations were inspired and closer to G-d, Orthodoxy tends to treat their interpretations of laws as equally binding, so there is not as much room for change by later generations. The Conservative movement respects the tradition, but does not see it as equally binding and thus later generations can interpret the biblical laws in other, generally more lenient ways.
In practice, there is a lot of variation, even in terms of belief. This is true of both communities, but probably to a greater extent in the conservative movement, where I expect if you asked most people who belong to conservative congregations "What does Conservative Judaism believe about the written and oral law, respectively?" they probably wouldn't be able to answer and some wouldn't be sure what the oral law is. That would, however, probably not be true of the types of conservative Jews who are regular attending services, who would probably have a somewhat firmer grasp, whether or not they themselves subscribed to these positions (I would say that overwhelmingly, conservative Jews do not believe that the Bible is the direct word of G-d). Probably the most visible difference, at a service, involves the status of women: almost all Conservative synagogues are now fully gender-egalitarian, whereas in most Orthodox services, men and women sit separately, and women do not have any ritual role during services.
In lifestyle, both groups, again, vary widely. On the right of Orthodoxy, or the "ultra-Orthodox," you have certain groups that are living more or less isolated lives of extremely stringent observance. Many of these groups have very high rates of poverty, as they have many children and the fathers often study Torah rather than getting jobs outside the community, which their religious based educatino may not have prepared them for anyway. Other ultra-Orthodox groups - namely, the Lubavitch/Chabad -- mix more with the world, but still maintain a very strict standard of observance that infuses every facet of their lives.
Modern Orthodox Jews more or less live in the everyday world. A lot of them would dress in ways that might make them identifiably Jewish to outsiders (i.e, wearing a yarmulke/skullcap), but almost all of them go to secular universities, hold secular, usually professional jobs, etc. As in any community, some people may theoretically ID as Modern Orthodox because they grew up in the community and still believe nominally in its precepts, even though their observance has become lax in fundamental ways. This would be less possible, however, in an ultra-Orthodox community ,where deviance from the norm is not tolerated. On the left wing of MO, there are now people testing some of the boundaries of halacha (Jewish law) involving things like women's participation and the status of homosexuality; these people are not willing to go as far as the other movements because they still take a limited view of how much power later generations have to overrule earlier ones, but they are looking for ways within halacha to advance on social justice issues.
On the rightmost edge of the Conservative movement, you have people who are indistinguishable from a MO person in terms of observance, but may be committed to full gender egalitarianism. On the left, you have people who may observe almost no aspects of traditional Judaism, but when they go to a service, prefer the more traditional liturgy of Conservative Judaism to Reform Judaism's more flexible services. But on average, I'd say the active conservative Jew is someone for whom Judaism is the core of their identity and a big part of their lives, but not necessarily something that is guiding their daily actions to the same extent as an Orthodox Jew: they celebrate Shabbat and holidays with varying levels of stringency, may be active in Jewish social and volunteer organizations, etc, but on a random Tuesday, they probably aren't going to go to daily prayers, and even if they follow some dietary laws, they probably won't have to stress about finding the nearest kosher restaurant because they're willing to eat vegetarian food without a kosher certification. They may observe traditional Shabbat restrictions against all forms of labor (including using electricity, driving, etc), or they may make a practice of doing the Friday night rituals at their family dinner, go to services, but then be perfectly willing to go to a movie later in the afternoon.
Hope this is helpful. Thank you to everyone who has expressed their well-wishes to the community - while I have no Pittsburgh connections, the Jewish community is small enough that this hits close to home for all of us, and it is heartening to see so many people showing their support.
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