The foil is a much misunderstood weapon. From the point of view of many historical fencers it is much maligned, and even from modern fencers it is misunderstood due to the rules which are associated with it. The following discussion attempts to shed some light on the use of the foil not only to the modern fencer, but to fencers in general as it can be a most useful tool when it is approached from the correct perspective.
The original purpose of the foil was as a training weapon for the smallsword. It was a lighter version created so that the weapon could be held for an extended period of time so more training could be done. Clearly it was blunted so that it could be used in training. The "right of way" rules which are associated and also its target area, limited to the torso, were both designed to protect the individuals who were practicing with it to prevent injury to them.
When the foil was first introduced, masks were not being used so removing the head from target was an effort to prevent damage to the vulnerable face. The "right of way" rules encouraged fencers to ensure that they had a defence presented before they launched an attack at their opponent, thus preventing two fencers from impaling one another and losing control of where the points of the weapons went. This training tool encouraged the fencer to prepare a proper defence, and penalised the fencer who did not defend themselves before attacking.
The foil's prime current use is in modern fencing where it is recognised as one of the three weapons used. This is the weapon which every beginner should start with as it teaches all of the basic fencing actions with the point and teaches the fencer form in these actions. Further, with the "right of way" rule, as it was previously stated, teaches the fencer to defend themselves before attacking. The foundation of a good modern fencing career starts with the foil. All of the actions of the foil transfer to the epee, and the "right of way" rules are used in sabre, with the addition of cuts.
The historical fencer can use the foil for its original purpose, as indicated, for practicing smallsword, but this is not the only purpose that the foil can serve. The nature of the weapon means that actions need to be performed with precision for them to work, so it encourages the individual who practices with the foil to increase their accuracy in their technique. This weapon has utility in practicing for rapier actions as well.
If the foil is used for practicing rapier actions one will find that accuracy in technique is required. There is no weight in the weapon to compensate for sloppy technique. Blade engagement actions need to be made accurately and so do actions on the blade. This is only accentuated where the foil is used for practice against a partner using a rapier, but if the actions are accurate in their performance then the actions will succeed. It is not recommended that the foil be taken against the rapier in any sort of antagonistic scenario as the foil is simply much too light physically to stand against the rapier and has a higher chance of breaking dangerously in this sort of scenario.
The foil is especially useful for those times when a person is restricted due to some illness or injury. The foil is much lighter than most other weapons and thus can still be carried and used for practice. I have done this myself when I was not able to use a rapier due to an injury and found that using the foil, I was able to participate in training exercises. I further found that such participation was useful because it made me perform the actions properly, due to the nature of the weapon that was being used.
To understand the use of a weapon means that a person must understand the weapon. This requires looking into the purpose of the weapon. The foil is a practice weapon and should be used as such. It is an often forgotten, and often maligned weapon that can be most useful to all sorts of fencers, should it be examined from the correct perspective. Take another look, have another go, the foil is more useful than you realise.