Telling the Truth is the Best Goal
By Father Kenneth Wasilewski
The definition used by the Catechism of the Catholic Church for a lie (which is taken from St. Augustine) seems straightforward enough: “speaking a falsehood with the intention of deceiving.” But that definition can still leave us with some questions about whether or not certain actions actually constitute a lie. 
For example, what if I say something that I know isn’t true in order to throw a surprise birthday party for someone? Or what if I tell a story I know isn’t true as part of a joke? What if I tell my children that it was Santa Claus who brought the presents at Christmas time? Or what if I eat the cookies they left for him and tell them it was him who ate them? Do situations like these actually constitute lying in the proper sense? 
From a moral standpoint these things don’t amount to sins. While they may involve deception and falsehood, they are typically done in connection with entertainment or custom and without any real harm being intended or inflicted. Moreover, from the very beginning there is an intention to eventually reveal the truth or let it be known at the proper time. Both the falsehood itself and the deception are temporary by design. In fact, examples like these are sometimes referred to as “jocular lies” in order to distinguish them from those that do constitute a moral offense. On closer inspection these are quite different from an actual sinful lie where the intention is to continue both the falsehood and deception perpetually. 
An actual lie is typically told to lead someone into error, and to leave them there. Nevertheless, there have still been some holy people over the centuries who are a little uncomfortable with permitting even “jocular lies” without some caution. Some would warn about forming a habit of telling jocular lies simply because they do involve some deception and falsehood. Some have argued that forming such a habit can make the road to telling more serious lies easier to go down. Some have also argued that while they may not constitute a “sin” they can still be deemed an “imperfection” because we’re still willing to use falsehood and deception. Nevertheless, they don’t typically constitute an actual sin under reasonable and normal circumstances. It would take a situation where one is telling jocular lies in an egregious, uncharitable or harmful way for them to rise to the level of being considered sinful.
That last consideration, whether or not they’re harmful, is an important criteria in judging the seriousness of any lie. In fact, the catechism points this out in section 2484. Along with the harm suffered, it also mentions other criteria in our moral evaluation that must be considered. Namely, the nature of the truth it deforms, the circumstances and the intentions of the liar. 
It’s especially problematic when the lie can mean serious or even deadly consequences for the ones being deceived (CCC 2484, 2485). We can think of some examples to illustrate this. Think for example of the potential ramifications of someone testifying in court. If a witness knowingly gives false testimony (thereby perjuring himself or herself) it can potentially have a very serious effect on the outcome for the accused — possibly contributing to an unjust sentence. 
Contrast that with a less serious lie (although still a lie!) when someone pays a compliment falsely — perhaps saying that someone looks nice, when the person doesn’t actually think so. Even though both cases involve lies, we can see there are different degrees of harm done in each case. It’s not to say that the smaller lies are ok, it’s just that we can notice a difference in the amount of harm done in each case. Perhaps the best way to avoid causing harm through lying — whether a lot of harm or just a little — is to continually strive to be as truthful as possible in all situations.