> Yes... But it is very much not true that a court requires a literal monopoly in order for them to find behaviors to be anti-competitive. All that needs to happen is for a company to have significant market power.

If by literal monopoly you mean a single firm that controls 100% of the market, then we don't disagree, as I never suggested that was required. However, proving a section 2 monopolization claim does require proving the existence of monopoly power.

A company is considered to have monopoly power when it has a significant degree of market power. A literal monopoly is not required, however courts have typically not found monopoly power when market share is below 50% either.

> And in the US, as of last month, if you are keeping up with the most recent data regarding market share, Apple has about 50% of the US market.

Can you cite a specific source? I've seen all sorts of different numbers but some seem to be based on web browser usage or device shipments which is not quite the same as active users.

> That is a pretty reasonable argument, that has a real, non-negligible, possibility of standing up in court.

While I certainly think it's possible, the case becomes a lot easier if the company has 90% market share (as Microsoft did) compared to 50% market share.

In other words, I find the comparison to the Microsoft case lacking because with 90% market share it was more or less accepted by both sides that Microsoft held monopoly power in the operating system market, whereas in this situation it's much more debatable. To quote from my previous link:

In determining whether a competitor possesses monopoly power in a relevant market, courts typically begin by looking at the firm's market share.(18) Although the courts "have not yet identified a precise level at which monopoly power will be inferred,"(19) they have demanded a dominant market share. Discussions of the requisite market share for monopoly power commonly begin with Judge Hand's statement in United States v. Aluminum Co. of America that a market share of ninety percent "is enough to constitute a monopoly; it is doubtful whether sixty or sixty-four percent would be enough; and certainly thirty-three per cent is not."(20) The Supreme Court quickly endorsed Judge Hand's approach in American Tobacco Co. v. United States.(21)

Following Alcoa and American Tobacco, courts typically have required a dominant market share before inferring the existence of monopoly power. The Fifth Circuit observed that "monopolization is rarely found when the defendant's share of the relevant market is below 70%."(22) Similarly, the Tenth Circuit noted that to establish "monopoly power, lower courts generally require a minimum market share of between 70% and 80%."(23) Likewise, the Third Circuit stated that "a share significantly larger than 55% has been required to establish prima facie market power"(24) and held that a market share between seventy-five percent and eighty percent of sales is "more than adequate to establish a prima facie case of power."(25)

It is also important to consider the share levels that have been held insufficient to allow courts to conclude that a defendant possesses monopoly power. The Eleventh Circuit held that a "market share at or less than 50% is inadequate as a matter of law to constitute monopoly power."(26) The Seventh Circuit observed that "[f]ifty percent is below any accepted benchmark for inferring monopoly power from market share."(27) A treatise agrees, contending that "it would be rare indeed to find that a firm with half of a market could individually control price over any significant period."(28)

In other words, 50% is near the bottom of the range, and is going to be hotly contested.