"You're right," David says, when Roy is done speaking.

"Wait a minute," Simon complains. "You haven't heard my side."

After Simon finishes talking, David proclaims, "He's also right."

"How can they both be right?" asks Joe, in exasperation. "Their arguments are diametrically opposed to one another."

"You're right, too!" David replies.

Just how old is that joke? Well, it hasn't been found in the Dead Sea Scrolls or inscribed on any clay slab. Yet it's not entirely far-fetched to believe that the joke is at least as old as the Jewish Calendar - some 3,300 years - since a similar conversation could have taken place at the time the calendar was created.

Here's the argument. It's the first day of the Jewish month that we now call Nissan. The Jewish people are still enslaved in Egypt - but not for much longer because G-d is about to deliver them out of captivity. G-d says to Moses and his brother Aaron, "This month (Nissan) shall be the beginning of the months for you; it shall be the first of the months of the year for you" (Exodus 12:2).

In other words, G-d is instructing the Jewish people to make a new calendar. G-d then goes on to tell them the date the Exodus is going to happen, and that the people should remember this day for all time.

The task sounds simple enough. Just start counting the new year from the month of Nissan - instead of beginning the new year with whatever month they had been using as a starting point before - and put a gold star on the big day, which is the 15^th of Nissan.

But a few lines later - after the Exodus has occurred, and Moses is speaking to the newly freed people - we read that Moses commands the people to remember this day that happened in the month called "Aviv" (Exodus 13:4). Furthermore, Moses tells them, "You shall therefore keep this statute (remembering the Exodus) in its season from year to year" (Exodus 13:10).

From this we learn that the mitzvah of remembering the Exodus must be done during the season when the original Exodus occurred - in Aviv, which means "spring".

And that's where the problem begins.

The concept of a "month" is based upon the phases of the moon - a cycle that takes approximately 29 ½ days to complete. A new month begins with a new moon, a tiny sliver in the sky, and reaches its apex on the 15^th - when the moon is full. The seasons of the year, on the other hand, are determined by the earth's orbit around the sun. If a calendar is based on the lunar cycle, it can't be solar - and vice versa - because they are as different as, well, night and day.

So how should the Committee for Creating a New Jewish Calendar go about solving the problem of keeping Passover both in the spring and on the 15^th day of Nissan?

The argument in favor of a lunar calendar is that a holiday will always occur at the same point in the moon's cycle. This is important because the Exodus took place on a night when there was a full moon, which has a special significance for the Jewish people. Our fortune as a nation is often compared to the phases of the moon - for just as the moon always renews itself, so, too, does G-d promise us that we will always experience a renewal - even after the darkest night. Therefore, if we want to re-experience the Exodus on a night when the moon is full - symbolic of the time when our good fortune is at its peak - a lunar calendar is definitely the way to go.

However, in a regular 12-month lunar calendar, which consists of only 354 days, holidays will float through the months and occur at different seasons. The prime example of a lunar-based calendar is the Moslem calendar, in which the month of Ramadan, a holy month for the Moslems, can - and eventually does - occur in every season. Since Passover must take place in the spring, a lunar calendar is therefore out of the question.

In a solar-based calendar, which is the 365-day calendar used by the western world, we know that Memorial Day (in America) will always signal the beginning of summer and Labor Day means that fall is on its way. It could also help us fix Passover in the spring. But this calendar is hopeless for figuring out when the new moon or a full moon will occur, since the first day of the solar month is not at all connected to the lunar cycle.

It seems, therefore, that G-d was asking the Jewish people to do the impossible: join together two opposing concepts - lunar and solar - to create a new kind of calendar.

This request was revolutionary then, and it is still revolutionary today. Because this request was not just about creating a new calendar - G-d was asking the Jewish people to create a whole new way of looking at the world.

Most of the world's philosophers have tended to divide the world into dichotomies. Something is either black or it's white, and you're either in one camp or the other.

For instance, a favorite philosophical question asks, "Is a person body or soul?"

Some religious traditions have suggested that our purpose in life is to totally transcend the body and the material world and become all soul. They recommend practices such as fasting, seclusion and meditation to reach the higher truth.

Some not particularly religious traditions, on the other hand, adamantly proclaim that we are only body and the physical world is all there is. The old beer slogan, "Grab all the gusto you can get," could be their motto.

Judaism's answer to the question, in contrast, is an enthusiastic, "Yes!" Since G-d is one and He is the source of everything, there must be a way to reconcile these seemingly opposing forces.

Do we have body that has very real needs that should be listened to? You bet. Do we have a soul that longs for something higher, and has an awareness of the eternal in this transitory world? Absolutely.

Like David in the joke told above, Jewish thinkers have listened to the arguments of each side and concluded, "You're both right." Body and soul both very much exist, and in this world, at least, you can't have one without the other and remain alive. In fact, it is this interplay between the physical and spiritual, with all its frictions, that makes a human being human - and not an animal or an angel - and allows us to fulfill our life's purpose.

Another big argument that has been discussed for ages involves the question of fate vs. free will. Is our life's path determined at birth or are we totally free to choose the direction our lives will take?

Again, Judaism's answer is, "Yes." G-d most certainly has a plan for this world, yet we are free to choose our role in it.

A prime example of how this works is the Purim story. Haman, chief advisor to King Ahashverus, has issued an edict to kill all the Jews living within the Persian Empire. G-d has arranged things beforehand, so to speak, so that Esther, who has kept her Jewishness a secret, has to marry King Ahashverus. Thus, when Haman announces his plan to kill the Jews, a rescuer - Queen Esther - is already in the palace and in a position to stop Haman. All she has to do is play her part - and that's the moment where free will steps in.

At first, Esther uses her free will to refuse to stick her neck out for her people. She is afraid she might anger the king, and get her own head chopped off (it's happened before in this palace). It is only when her Uncle Mordechai reminds her that G-d has a plan to save the Jews - with or without her help - that Esther reconsiders and agrees to be the catalyst for putting this plan into action.

This ability to take seeming paradoxes of life and create a unity out of them has characterized the Jewish people since their very beginnings as a nation - and it has preserved us till this very day. For it is no accident that the first mitzvah-task we were given was to solve the riddle of the lunar/solar calendar. In the way this commandment is phrased in Hebrew, there is a hint as to how to solve not just the calendar riddle, but also another seeming paradox - how can the Jewish people be both the oldest nation in the world and the youngest?

Back in Exodus 12:4, G-d tells the people, "This month shall be the beginning of the months for you; it shall be the first of the months of the year for you." Why does G-d need to say both parts of the phrase? What's the difference between being the "beginning of the months" and being the "first of the months of the year"?

In Hebrew the word for month is "chodesh," which has the same three-letter root as the word for "new" (chadash). On the other hand, the word for "year" in Hebrew is "shana," which has the same root as the word for "old" (y'shan).

The challenge of the Jewish calendar, therefore, is to join together the two opposing forces of old and new.

Some cultures, such as the Egyptian culture the Jewish people had been enslaved in, make their people captives of the past. Others, such as American culture, entice their citizens to worship at the altar of the new.

Judaism is unique in that it asks us to be both old and new at the same time.

Yes, during our holidays we commemorate events that happened thousands of years ago. But we do so because we know that by living in tune with the Jewish calendar, we can plug into the same spiritual energy that transformed and elevated our ancestors and use this energy to recharge our own spiritual batteries.

Every Passover - in fact, every Jewish holiday - is a call to wake up, change and grow. Whether we are retelling the story of the Exodus or lighting the Chanukah menorah, each holiday gives us a unique opportunity to re-ignite that spark of holiness that is found in every soul.

What we experience on an individual level, we also experience on a national level. Since we know that just as Passover recalls the past redemption from Egypt, it also foretells the future, final redemption, there has never been a time in our history - no matter how dark - when we have given up hope.

It is this ability to be both deeply connected to the past and committed to making each day "new and improved" that has enabled the Jewish people to pass over 2,000 years of exile, persecution and Holocaust and always retain a youthful sense of optimism about the future.

It's also what makes a calendar Jewish.

(N.B. So how does the Jewish calendar solve the lunar-solar paradox? The Jewish calendar is, indeed, based on the lunar cycle. But because a lunar calendar's "year" has only approximately 354 days - eleven days less than a solar calendar - our calendar has to somehow make up for this loss. We do this by creating leap years seven times during a 19-year cycle, where a 13^th month (Adar II) is added at the end of the year. In this way, the calendar is able to remain in tune with both the lunar and solar cycles.)