The verb δύναμαι occurs more than 400 times in the Bible in Greek. Of those believers who have heard teaching about this important and widely used verb, many probably have the notion that it signifies an inability to do something in the sense that a person is not capable of doing something.
Although the verb does express that idea in numerous passages, it does not always do so. The following passages show that the verb is used at times to express inability due not to a lack of capability but rather to a lack of authority to do something:
LXE Deuteronomy 16:5 thou shalt not have power to sacrifice the passover in any of the cities, which the Lord thy God gives thee.
BGT Deuteronomy 16:5 οὐ δυνήσῃ θῦσαι τὸ πασχα ἐν οὐδεμιᾷ τῶν πόλεών σου ὧν κύριος ὁ θεός σου δίδωσίν σοι
KJV Deuteronomy 16:5 Thou mayest not sacrifice the passover within any of thy gates, which the LORD thy God giveth thee:
LXE Deuteronomy 17:15 thou shalt surely set over thee the ruler whom the Lord God shall choose: of thy brethren thou shalt set over thee a ruler; thou shalt not have power to set over thee a stranger, because he is not thy brother.
BGT Deuteronomy 17:15 καθιστῶν καταστήσεις ἐπὶ σεαυτὸν ἄρχοντα ὃν ἂν ἐκλέξηται κύριος ὁ θεός σου αὐτόν ἐκ τῶν ἀδελφῶν σου καταστήσεις ἐπὶ σεαυτὸν ἄρχοντα οὐ δυνήσῃ καταστῆσαι ἐπὶ σεαυτὸν ἄνθρωπον ἀλλότριον ὅτι οὐκ ἀδελφός σού ἐστιν
KJV Deuteronomy 17:15 Thou shalt in any wise set him king over thee, whom the LORD thy God shall choose: one from among thy brethren shalt thou set king over thee: thou mayest not set a stranger over thee, which is not thy brother.
In both passages, the verb signifies inability due to divine prohibition and not to an intrinsic lack of capacity to do the actions in view: The Israelites were physically capable of offering the Passover anywhere, but God did not permit them to do so except in the place that He assigned (16:5). Similarly, they could have set a stranger over them as king, but God did not authorize them to do so (17:15).