The Talmud tells us (Makkot 23b) that, at Sinai, G‑d transmitted 613 mitzvot toMoses—248 positive commandments (dos) and 365 negative commandments (don'ts). When counting, however, we find that there are many more than 613 biblical obligations and prohibitions. Thus we need to explain the formula by which we determine whether a particular precept is counted as part of the 613 or not.
Maimonides used 14 principles to make this determination:
Do not count Rabbinic Commandments in this list. E.g. lighting Chanukahcandles or reciting the Hallel.
Indeed, this seems obvious, for the Talmud says that 613 mitzvot "were given to Moses at Sinai," and rabbinic mitzvot were not instituted until later dates. But in truth, we follow rabbinic rulings because of a biblical mandate: "You shall not divert from the word they tell you, either right or left" (Deuteronomy17:11); and as such, before performing a rabbinic mitzvah, we say a blessing in which we thank G‑d for "sanctifying us with His commandments and commanding us to..." Nevertheless, the individual rabbinic precepts are not counted as part of the 613 (and, are considered "rabbinic," a classification that has certain halachic implications).