When he (a king) thinks that his hereditary army is more than he requires for the defence of his own possessions or when he thinks that as his hereditary army consists of more men than he requires, some of them may be disaffected; or when he thinks that his enemy has a strong hereditary army famous for its attachment, and is, therefore, to be fought out with much skill on his part; or when he thinks that though the roads are good and the weather favourable, it is still the hereditary army that can endure wear and tear; or when he thinks that though they are famous for their attachment, hired soldiers and other kinds of troops cannot be relied upon lest they might lend their ears to the intrigues of the enemy to be invaded; or when he thinks that other kinds of force are wanting in strength, then is the time for taking the hereditary army.