The lengthy history of Hasidism, the numerous schools of thought therein, and particularly its use of the traditional medium of homiletic literature and sermons – comprising numerous references to earlier sources in the Torah, Talmud and exegesis as a means to grounding oneself in tradition – as the almost sole channel to convey its ideas, all made the isolation of a common doctrine highly challenging to researchers. As noted by Joseph Dan, "Every attempt to present such a body of ideas has failed". Even motifs presented by scholars in the past as unique Hasidic contributions were later revealed to have been common among both their predecessors and opponents, all the more so regarding many other traits that are widely extant – these play, Dan added, "a prominent role in modern non-Hasidic and anti-Hasidic writings as well". The difficulty of separating the movement's philosophy from that of its main inspiration, Lurianic Kabbalah, and determining what was novel and what merely a recapitulation, also baffled historians. Some, like Louis Jacobs, regarded the early masters as innovators who introduced "much that was new if only by emphasis"; others, primarily Mendel Piekarz, argued to the contrary that but a little was not found in much earlier tracts, and the movement's originality lay in the manner it popularized these teachings to become the ideology of a well-organized sect.