“And David took from him a thousand chariots, and seven hundred horsemen, and twenty thousand footmen: and David houghed all the chariot horses, but reserved of them for an hundred chariots.” (2 Samuel 8:4, KJV)
This concerns the battle between David and Hadarezer. The KJV follows the Masoretic text and says that David captured “a thousand chariots, and seven hundred horsemen.” The NASB and ESV say, “1,700 horsemen” without mentioning chariots. The NIV departs from the Masoretic text and says, “a thousand of his chariots, seven thousand charioteers [horsemen].” 1 Chronicles 18:4, a parallel passage, in the KJV, NASB, ESV and NIV all say that David captured “a thousand chariots, and seven thousand horsemen”; so there were certainly a thousand chariots. That leaves us with the question as to why 2 Samuel 8:4 in the KJV says “seven hundred horsemen” whereas 1 Chronicles 18:4 says “seven thousand horsemen.”
We can take two steps to solve this mystery. The first step is to understand that horsemen and footmen were not exclusive categories, but that horsemen were a subset of footmen. Soldiers who were trained to ride horses were usually trained first as ground infantry just as armored vehicle operators of the USA Marines are all initially trained as ground infantry. There is a clear example of this double role elsewhere in scripture. 2 Samuel 10:18 describes a battle where David slew “forty thousand horsemen” of the Syrians (KJV, NASB, ESV). 1 Chronicles 19:18, describing the same event, says that David slew “forty thousand footmen” of the Syrians (KJV, NASB, ESV). 2 Samuel 10:18 and 1 Chronicles 19:18 read together suggest that the horsemen and the footmen were the same men just described differently. There were not 80,000 men in total but rather 40,000 men who took on double roles as horsemen and footmen. Hence in the case of the Syrians the subset (40,000 horsemen) occupied the entire set (40,000 footmen). Going back to the battle against Hadarezer, when 2 Samuel 8:4 says that there were “seven hundred horsemen, and twenty thousand footmen,” there were not 20,700 men in total, but rather 20,000 men of which 700 were considered horsemen by the author of 2 Samuel. Likewise, when 1 Chronicles 18:4 says that there were “seven thousand horsemen, and twenty thousand footmen,” there were not 27,000 men in total, but rather 20,000 men of which 7000 were considered horsemen by the author of 1 Chronicles. Listed categories that are connected by the conjunction “and” do not have to be exclusive categories. For example, the Bible often uses the phrase “Judah and Jerusalem” even though Jerusalem is part of Judah. Listed categories that are connected by “and” can overlap in what they refer to. Thus “x horsemen, and twenty thousand footmen” means that there were x number of entities that qualified as horsemen and twenty thousand entities that qualified as horsemen, not that there were two exclusive categories of horsemen and footmen.
The second step to solving the mystery is to see that the difference between 700 and 7000 horsemen is due to “horsemen” being a floating label. The designation, “horsemen” is a floating label because it attaches when a man is on a horse, and could detach when a man is no longer on a horse. Chariots can always be called “chariots” (thus 2 Samuel and 1 Chronicles both agree that there were a thousand chariots). Footmen can also always be called “footmen” since all chariot riders are trained with the basics of ground infantry (thus 2 Samuel and 1 Chronicles both agree that there were 20,000 footmen). However, horsemen are not always horsemen. If at the start of battle there were 7000 men on horses, one historian can say that David captured 7000 horsemen in battle. However, if at the end of the battle 6300 horses go out of commission and only 700 men remain on horses, then another historian can say that David captured 700 horsemen in battle. The discrepancy in numbers is due to the different perspectives of the historians. The author of 1 Chronicles still referred to the men who lost their horses as “horsemen” whereas the author of 2 Samuel only referred to the men still on horses as “horsemen.” This discrepancy could have arisen if the historian of 1 Chronicles got his number from a headcount of horsemen prior to battle (as the two sides squared off against each other) and the historian of 2 Samuel got his number from a post-battle headcount. Both accounts are correct according to their own perspectives. There is evidence that different historical sources were used in the two books. For example, as mentioned earlier, the superficial difference between 2 Samuel 10:18 (“forty thousand horsemen”) and 1 Chronicles 19:18 (“forty thousand footmen”) demonstrates that one account is not a mere duplicate of the other.