I have been fortunate to know many couples who have been married 40 years or more. In some couples, the two are like the proverbial two peas in a pod. Sometimes the two are so different, it makes other people marvel that they have been together for decades. Over the last year, I’ve been talking to 7 married couples who are happily together after many, many years to see if there are any identifiable commonalities among them.

There are. Straight or gay, regardless of background, the people in each couple have shared ideas of what they expect from themselves and each other. It may sound unromantic, but early on they made what I’m calling a kind of “contract.”

For some, it was explicit; the result of hours of talking and working things through during courtship and the early years of marriage. For others, it has been unstated but understood. Somehow, they just got each other from the beginning. Regardless, these marriages have withstood the ups and downs of life over decades because both members have lived up to their shared expectations about the areas they agreed were most important.

Each couples’ “contract” includes most of the following topics, although the order of importance varies by couple. Do note: This was not a formal study. It is an account of what emerged in conversations with elderly friends and their couple friends as we talked about their experience.

  • Their roles: Regardless of others’ feelings about the “rightness” of a particular style, happy couples found roles that are comfortable for them. Some couples were quite happy with what could be described as the traditional nuclear family, with one person being the primary homemaker and parent and the other providing the financial support. Other couples would be appalled by that idea — and created a more equalitarian style. Others agreed on something in-between. It’s the agreement, not the arrangement, that made them comfortable.
  • How decisions are made: There’s an old joke: An interviewer asks a couple how decisions are made. “He makes the important decisions.” said the wife. “I make the minor ones — like where we should live, how our money is managed, and how to discipline the kids.” “So what important decisions does your husband make?” asked the interviewer. “Well,” sahe said, “things like whether Russia or China is a bigger threat, and if we should be worried about robots taking over our jobs.” For most of the couples, it was much more complicated than that. But it was making a clear decision about how decisions were to be made that made life easier. One woman said she found it freeing to know what decisions needed a conversation and which ones were her responsibility.
  • Frequency and style of sex: Some couples I interviewed have lived happily with little sex. Some agreed that sex every morning is the right start to the day. One couple in their late 80s joked they have as many positions as the Kama Sutra. Others settled contentedly into one. What kept couples together is shared satisfaction with whatever they decided was right for them.
  • Fidelity: Fidelity is in the eyes of the couple. For some, sex with anyone else would have been a deal-breaker. For others, it’s been okay to have casual sex with other people but “don’t tell me about it.” They all stressed the importance of an agreement being a real agreement; not a concession; not a resignation. That agreement is sacrosanct. If one person were to unilaterally break the agreement, the relationship would be in serious trouble.
  • Money: Next to fidelity, all of the couples agreed that a lack of a clear understanding about how money is made, spent, and saved would have been a serious threat to their marriage. These long-married couples worked out their financial understanding early on.
  • Religion, politics, race, and culture: For two of the couples, their marriage has been what one described as “a cross-cultural experience.” The long-married couples who came from dissimilar backgrounds (religion, race, nationality, political views, etc.) have an abiding respect for each other’s beliefs and traditions. Their differences have been enriching and an endless and interesting topic of conversation
  • Relationships with extended family: Some couples welcomed their own aging parents or their adult kids or other relatives into their home for extended periods of time. Others find the observation by Mark Twain that “fish and relatives stink after 3 days” is true. Some people talk to their relatives weekly, even daily. Others have seen them for only on an annual holiday or two. For all of the couples, there was an agreement about the degree of influence by the older generation as well as agreement about their obligation to the extended family.
  • Relationship with friends: Is it okay for each to have their own friends or must all friendships be shared? Is it okay to have a best friend who is of the other sex — or does that threaten the marriage? One man in his 90s suggested that decisions about social relationships are related to a couple’s security in each other’s fidelity. “I trust her absolutely, so I have never had a problem with whom she spends time.”
  • Kids: Children do change almost everything. They take time, energy, and money. Priorities shift. These couples had a shared idea about whether to add children, how to raise them, and who should do what. Most who did have kids carved out a “date night” to ensure their coupleness didn’t get lost in the chaos of family life.

Regardless of the topic, I think what separates the long-married from relationships that don’t last is their commitment to their “contract” and their willingness to talk about it whenever one or the other thought there needed to be a change.

Change isn’t necessarily a threat. Sometimes change is forced by necessity; sometimes by experience; sometimes by the fact that people do grow up and grow into a different perspective about an issue. What was most meaningful to me in my conversations with these couples was the respect they had for each other and their commitment to meeting challenges and changes together. One elderly woman agreed. “But don’t forget to tell people,” she added, “a sense of humor really helps.”