Traditional voting system (by power/by order)

Prior to 1789 the Estates-General had not met since 1614. Traditionally the Estates-General would essentially vote as three seperate chambers (First, Second & Third Estates), and a majority in two of the three chambers was needed to pass a motion. This allowed the two privileged orders to vote in unison and override the wishes of the Third. This occurred despite the Third Estate representing roughly 98% of the population.

Demands to vote by head and double the Third's representatives

In 1789 the government came under immense pressure from the Third Estate (and the free press) to change the system of voting to 'by head'. This reform would essentially combine all of the Estates-General's delegates into one chamber and give each delegate a single vote (as is the case in many modern parliaments).

However, voting 'by head' was not enough to guarantee the Third Estate controlled the reformed Estates-General, as traditionally they would only have had 1/3 of the deputies. As a result, the Third Estate also called for the doubling of their representatives. The justification for this was that the Third Estate did comprise a huge majority of the population (roughly 98%). If the reforms went through, then half of the Estate-General's delegates would come from the Third, a quarter from the Nobility and a quarter from the Clergy. If liberally minded nobles and common priests joined with the Third, the 'nation' would control the Estates-General.

To answer your first question, if both reforms were not implemented, the aristocracy would control the Estates-General (there is an assumption here that the First Estate's delegation would be dominated by bishops and the higher-clearly, which did not actually occur in 1789 due to reforms by Necker that enabled common priests to vote (resulting in many common priests becoming delegates)). As a result, the traditional Estates-General would vote favourably for the privileged orders.

Public pressure & doubling of the Third's representative's prior to the Estates-General

After the Day of Tiles revolt in Grenoble in June 1788, the Vizille Assembly occurred in the Dauphiné. This was a provincial Estates-General for the Dauphiné. As the Assembly was held against the government's wishes (as a result of the successful revolt of Grenoble's populace), radical members of the Vizille Assembly implemented both reforms. Thus, as the debate waged at a national level as to whether or not the government would summon an Estates-General, a miniature, reformed Estates-General was active in the country. Furthermore, the Estates of Dauphiné called for a national Estates-General and the refusal to pay taxes until it was summoned. This piled on the pressure for Louis and Necker (who was recalled in August, 1788) to implement voting by head and to double the Third's representatives. As Historian Robert Johnson (1910) notes, “The effect of the resolutions of the assembly of Vizille through France was immediate. They were simple, direct, and voiced the general feeling; they also indicated that the moment had come for interfering in the chronic mismanagement of affairs. So irresistible was their force that Loménie de Brienne and the King accepted them with hardly a struggle.”

Having replaced Brienne, Necker had to decide whether the government would concede to the reforms (the government conceded an Estates-General just prior to Brienne's resignation). There is much historical debate as to whether Necker wanted to implement these reforms or if he was forced to by the unrest occurring across the countryside. To answer your second question, it is clear that the government did consider keeping the traditional format of the Estates-General a valid option (voting by power) and did consider the negative response this would illicit from the Third Estate (depending on the individual).

In fact, this negative response is why Necker doubled the Third's representatives in December 1788, according to Historian John Dalberg-Acton (1910).

“The agitation in the provinces, and the explosion of pent-up feeling that followed the unlicensed printing of political tracts, showed that public opinion moved faster than that of the two great conservative bodies. It became urgent that the Government should come to an early and resolute decision, and should occupy ground that might be held against the surging democracy. Necker judged that the position would be impregnable if he stood upon the lines drawn by the Notables, and he decided that the Commons should be equal to either order singly, and not jointly to the two. In consultation with a statesmanlike prelate, the Archbishop of Bordeaux, he drew up and printed a report, refusing the desired increase. But as he sat anxiously watching the winds and the tide, he began to doubt; and when letters came, warning him that the nobles would be butchered if the decision went in their favour, he took alarm. He said to his friends, "If we do not multiply the Commons by two, they will multiply themselves by ten." When the Archbishop saw him again at Christmas, Necker assured him that the Government was no longer strong enough to resist the popular demand.”

Thus, according to Dalberg-Acton, it was only because of the government's concerns regarding the Third Estate's reaction that they agreed to double the Third's representatives. However, Necker left the question of voting unresolved, hence why it was an issue at the commencement of the Estates-General. As the doubling of the Third's representatives was meaningless without voting by head, the issue remained at the forefront of public discussion.

Hopefully that helps to answer your questions.

The above issues, including the impact of the Vizille Assembly and whether Necker truly wanted to reform the Estates-General in a manner favourable to the Third Estate, are discussed in depth in Episodes 7 & 8 of the Grey History: The French Revolution podcast.

It was a question of how the votes would be counted. The Estates General of 1789 has 303 delegates from the clergy, 282 from the aristocracy, and 578 from the commoners. If they voted by head, then each delegate's vote would count the same and only a handful of the delegates from the other two estates would need to vote with the commoners for the latter's position to prevail on a question on which they were relatively united (most notably, extending the Taille tax to the other two estates).

But if they voted by power, then each estate's delegation would caucus together and take its own vote. Then each delegation would collectively cast a single vote, so for example a vote where 40% of each the first two estates and 90% of the third estate voted in favor would be recorded as 2 votes against, 1 in favor. This was how the Estates General had usually operated in its previous sessions, but those were 175 years in the past and the deails of their procedures were conseqiently obscure.

This raised objections not just because it meant the commoners would have a much harder time pushing through the reforms they wanted. Nor just because the commoners felt entitled to more than a 1/3 say in the affairs of the nation. The other big objection to the per-estate voting system was that it was a dishonest bait-and-switch: the third estate had been promised double representation (as they already had at this point in provincial assemblies), only to be told at the last minute that the double representaion would be meaningless when it came to the actual voting.