Generally, a collective that operates by consensus holds regular facilitated meetings at which proposals are submitted and discussed. At the end of each discussion, the facilitator will call for objections; if none are made, the proposal will be said to have passed by consensus. Yet, this process doesn't always guarantee that there really is consensus, as a lot depends on the power dynamics that come into play. For instance, if members are individually approached ahead of time and persuaded on the merits of the proposal, that's a manipulation of the process, as it bypasses the open forum, which is at the heart of consensus. Or, if an influential or intimidating member voices strong support for the proposal and exhibits annoyance or impatience with anyone who raises concerns, thereby restricting the free exchange of ideas and possibly influencing the final outcome, the decision will not have been made by consensus.
If some members do not have access to the information needed to make an educated choice but have to rely on the assurances of the proponents that their plan is sound, that, too, will essentially invalidate the consensus.
The issue is even thornier when proposals do not pass. In many instances, if unanimity cannot be reached, the issue will simply be dropped and the group will revert to the status quo. That means that the matter the proposal was designed to address will remain unresolved. That is not consensus. Consensus requires that all members declare the outcome of a discussion to be at least marginally acceptable. If someone proposes a change because he or she perceives a problem that needs addressing, that person cannot simply be overruled for the sake of group agreement.
Blocking, the prerogative by one or more persons to stop a decision that everyone else would choose to pass, is the one aspect of consensus that seems to be universally embraced. It does not mean, however, that one person can hold the collective hostage to his or her whims. Blocking must be used judiciously and not as a power play. More often, however, pressure is applied by the more domineering members of the group to urge someone NOT to block and not to voice dissent. Blocking puts one in the spotlight and easily casts one as a troublemaker, particularly when it means defying powerful members who have already privately persuaded the others to go along with their agenda. Members who have established themselves as de-facto leaders (yes, this happens all the time in egalitarian collectives) and who may have attracted a following within the group through charisma or persuasiveness, or by scoring impressive achievements for the organization, don't have to resort to blocking to kill a proposal. It's enough for them to display annoyance, irritation, or agitation with the suggested action, generating distrust among others. The right individual could destroy a proposal simply by frowning at the right times, sighing in exasperation, or laughing sarcastically. Clearly, this is not consensus.
Consensus is not just the end result of the group's decision-making process, or the part where a vote is taken and the vote is unanimous, barring any blocks or stand-asides. The consensus process has to be built into the entire structure of the group or organization and form the basis for all of its activities and basic operation. This is true for all egalitarian collectives, even those who accept some form of majority vote in their decision-making and may therefore not strictly be defined as operating by consensus.
The basic premise of consensus, and indeed of any egalitarian group, is that all members of the group are valuable, everyone's opinions deserve consideration, and everyone's input is necessary for the group's efforts to proceed, in a spirit of collaboration. It differs from the group process used by conventional organizations in that it does not set up an adversarial relationship where one side wins (often the majority, but just as often the side backed up by the most authority) and the other side loses. In consensus, argument is not engaged in to defend a position but to arrive at solutions that everyone can consent to. In order for everyone to freely give consent, there must be no coercion or unequal power. Thus the absence of hierarchy and authority is not an added stipulation to the structure of egalitarian collectives but is essential to the consensus process.