"Col. Fox explains that he does not mean that the regiments he enumerates are the fighting regiments, but that they are 300 regiments which evidently did considerable fighting. There may have been others which did equally good or better fighting but for the lack of other information he can only take those which sustained the heaviest losses, and he has made the line of demarkation on those regiments which lost over 130 killed and died of wounds. This may be unjust in many instances, but still the regiment which lost 130 men killed must have done some hard fighting."

In other words, Fox said, the fighting regiments are not the fighting regiments. The fighting regiments are something else. They are the regiments that suffered over 130 killed and mortally wounded. His criterion was single, unambiguous, and fairly easy to measure—its only limitation being less than perfect casualty counts. Fox might better have named his regiments "the suffering regiments"—or "the regiments with losses over 130 in killed and mortally wounded". But, even understood correctly, Fox's measure of "fighting", was hotly criticized. Herbert Valentine of the Twenty-Third Massachusetts Infantry wrote (08-23-1906), "Is it not unjust discrimination that places [regiments] in two classes by the use of a term that leads those who do not know the basis of discrimination to view the one class as superior to the other in that which goes to make up an efficient regiment, namely, its fighting quality?" B. [Orestes B.] Wright of the 132nd Pennsylvania was one of numerous complainants who objected to "the dictum of Col. Fox". Wright thought, in the paraphrase of the editors of The National Tribune, that "grading a regiment by the number lost in action—assuming that the more killed and wounded, the more brilliant and brave the work done"—is a false mode of grading. Wright went on,

"Heavy losses may be the result of great bravery and splendid work. Again, they may be chargeable to cowardice and inefficiency of officers and men. According to the standard of Col. Fox's fighting regiments, the least deserving are likely to be credited with the best work. To illustrate: The regiment to which I belonged fought over four hours in the battle of Antietam, and out of 800 men engaged it lost 30 killed and 114 wounded, many only slightly wounded. Again, this regiment in the charge at Fredericksurg, VA., Dec. 13, 1862, on Marye's Heights, out of 340 engaged lost 150 in less than 15 minutes. At Antietam, where it fought, the sunken road in front was literally filled with dead rebels, three deep in some places. This showed desperate fighting, and the wonder is that all were not annihilated, from the number of shots fired. The reason why our loss was so comparatively light was on account of our position, while the enemy, who were more exposed, lost heavily. At Fredericksburg, on the other hand, we were in one of the most exposed positions in making our change, and accomplished nothing, tho we lost so heavily... According to Col. Fox, the 132d Pa. will never be classed as a fighting regiment, yet it did all that was required of it during its term of service. It helped put down the rebellion and to restore the Union. The best could do no more" (November 22, 1906).

Naturally, in the 2000s, people—not all people—continue to think that Fox meant something like "fighting quality" by "fighting". A current website, focusing on a particular regiment, speaks of the regiment as being one of Fox's "Top 300 Regiments".

Of the four regiments brigaded together with the 51st Illinois for most of the war, the 22nd Illinois and 42nd Illinois were among Fox's three hundred fighting regiments. The 27th Illinois and the 51st Illinois were not.