Professional Liability of Lawyers in Netherlands (Part III)

Published on Nov 19, 2025

This article, the third in the four-part series on professional liability of lawyers in the Netherlands, explores causality and determination of damages. 

The previous two articles in this series addressed the "standard” that applies in the case of professional liability of lawyers and the legal framework that must be observed, as well as the ways these liability risks can be mitigated. This article discusses what should happen when a professional error has been made by the lawyer. In this case, the next step is to establish whether there is a causal link between the professional error made and the extent of damage caused, which can prove tricky and is frequently the subject of debate in professional liability cases. This following article will delve into the role of causation and the determination of damages. 

Causal link between professional error and damages: the "main rule” 

From article 6:98 of the Dutch Civil Code (DCC), it follows that damage is eligible for compensation if it has sufficient connection to the error that it can be attributed to the lawyer who made the error. This threshold is fulfilled when there is a conditio sine qua non relationship between the professional error and the damage and the damage is reasonably attributable to the professional error.

  • Conditio sine qua non relationship 

To establish whether there is a conditio sine qua non relationship between the professional error and the damage, a comparison must be made between the actual situation in which the professional error was made and the hypothetical situation in which the error was not made. The determining factor is whether the creditor would have been in a better position if the professional error was not made. In this regard, 100% certainty can rarely be achieved. The condition sine qua non relationship is proven if the Dutch court rules that there is "a reasonable degree of probability” that the damage resulted from the professional error.

  • Reasonably attributable

As mentioned above, the damage must be reasonably attributable to the professional error. This limitation is important because any action may have endless consequences, but it is undesirable that all the adverse consequences will be "charged” to the original "causer”, even if there is a conditio sine qua non relationship between his actions and these consequences. Relevant points of view in assessing whether in the specific case the damage can reasonably be attributed to the professional error include: 

  • the nature of the norm violated; 
  • the liability and damages; 
  • the foreseeability of damages; and
  • the capacity and attitude of the parties involved. 

In 1981, Dutch professor Brunner established subrules for evaluating this attribution question. For the professional liability practice, the following subrules are most relevant: 

  • the more likely the consequence is (based on previous experience), the broader the attribution;
  • in case of violation of norms (e.g. traffic and safety) aimed at preventing personal injury, attribution is more likely to be justified;
  • it is easier to attribute personal injury than property damage, and property damage is easier to attribute than pure financial loss; and
  • the greater the blame, the broader the attribution.

Based on the main rule of article 150 of the Code of Civil Procedure (CCP), the burden of proof of the causal link between the professional error and the damages lies with the claimant. There are, however, some instruments under Dutch law that are exceptions to this main rule and can assist a claimant with causal uncertainty and prevent an unjustified denial of a claim. These include:

  • alternative causation;  
  • different allocation of burden of proof based on reasonableness and fairness; 
  • judicial presumption (in Dutch: "rechterlijk vermoeden"); 
  • rule of reversal (in Dutch: "omkeringsregel"); and 
  • proportional liability.

Determination of (the extent of) damages

Once the conditio sine qua non relationship is established, another phase begins. In this phase the judge estimates the (extent of the) damages, by considering which specific damages can be attributed to the professional error. This often is determined through a so-called trial within a trial in which a judge considers hypothetical scenarios and investigates how a case would develop without the error. By comparing the actual situation with the hypothetical situation in which the professional error did not occur, the damage is estimated.

The "main rule” is that the creditor must state the extent of the damages and prove this in the event of a substantiated dispute. Although article 6:97 DCC states that the court enjoys freedom in determining damages, generally damages are determined concretely, which means that the amount of the damages is determined as precisely as possible based on the concrete circumstances of the case. For each item of damage, it must be determined whether it is conditio sine qua non related to the professional error, whether the damage can be reasonably attributed, whether the damage is actually the amount as stated and whether the damage is reasonable. If it is not possible to determine the damage precisely, the court may estimate the extent of the damages based on article 6:97 DCC. Even then, damages are determined as much as possible based on the concrete circumstances of the case.

In exceptional cases (i.e. designated by law or by the court), an abstract damage assessment will take place. This means that damages are determined based on objective factors. An example is statutory interest, which is compensation for damages resulting from the delay in paying a sum of money. The advantage of an abstract damage assessment is that it is usually easier and cheaper than a concrete damage assessment. The downside, however, is that it requires the debtor to pay more damages than it actually caused.

Tenet of lost opportunity 

A special form of damage assessment is the "tenet of lost opportunity”. In this situation, the professional error is established, but it is uncertain how the future would have looked had the professional error not been made. The starting point is that the professional error actually resulted in damage (i.e. the loss of the chance for a better outcome). The tenet of lost opportunity is about establishing the scope of this chance (i.e. the damage).

The tenet of lost opportunity has been accepted by the Supreme Court in cases where a lawyer failed to file an appeal in civil appeal proceedings in a timely manner (ECLI:NL:HR:1997:AM1905; ECLI:NL:HR:2007:AZ0419) or failed to initiate legal action within the appropriate timeframe (ECLI:NL:HR:2007:AZ6541). In such cases, the professional error is established. It is, however, uncertain whether the appeal or claim would have resulted in success for the client, which means the extent of the damages is uncertain. In such cases, the court can determine damages by estimating the chances the client may have had in appeal proceedings. The same applies for a claim. Application of the tenet of lost opportunity requires a conditio sine qua non relationship between the liability-creating event and the loss of the chance of success. 

According to the Supreme Court, the function of the tenet of lost opportunity is to provide a solution for situations in which there is uncertainty whether an established professional error caused damages because it cannot be determined whether the chance of success would have actually materialised in the hypothetical situation where the professional error did not take place. 

Conclusion 

This article discussed the role of causation and the determination of (the extent of) damages in case of a professional error. In professional liability cases, these topics are often discussed. If the professional error has been established, it is often difficult for the claimant "to go through the following hoop” and prove causation between the professional error made and the (extent of the) damage caused. Under Dutch law, some instruments are developed to redeem causal uncertainty and to prevent an unjustified denial of a claim. In conclusion, the "tenet of lost opportunity” is considered an important and relevant instrument when professional errors are made by lawyers. This instrument is not a causation question but an application of a special form of damage assessment closely related to the causality issue. 

The next and last article in this four-part series will address the procedural aspects of a settlement of a professional liability claim.

For more information on this article and the professional liability of lawyers in the Netherlands, contact your CMS client partner or the CMS experts who wrote this article.