It is the gravitational gradient which causes tides. Because the gravitational pull of the Moon or Sun is slightly greater on the near side of the Earth than the far side, there is a tendency for the Earth to be stretched out into a paraboloid which bulges towards and away from the Moon or Sun. The tidal effect of the Moon is about twice that of the Sun.

The Earth's rotation averages out the stretching effect around the equator to produce a pole to pole flattening effect. This is in addition to the centrifugal flattening effect caused by the Earth's rotation on it's axis. The twice daily tides are much smaller than the additional equatorial expansion because of the inertia of the oceans which also gives rise to a 90 degree phase lag between high tide and the Moon's position in the sky.

Remember, it's only the difference in gravity or gravitational gradient that matters - the mean gravitational pull doesn't affect the situation locally as the Earth is in free fall in the Moon's or Sun's gravitational field i.e the mean gravitational pull on the Earth is cancelled out by the orbital centrifugal force (the Earth is orbiting the centre of gravity of the Moon and Earth combined which is about 3000 miles from the Earth's centre).

If the Earth were to be held at a fixed distance from the Moon and the Moon's orbital period were slowed down or speeded up, then, respectively, mean gravitational pull or centrifugal force would dominate and there would be a daily tide superimposed on the twice daily tides.

you are getting the idea "if the Earth and the Moon were simply held apart by a big stick, and not rotating, would there still be a bulge of water on the side away from the moon?" No! I hope the following will be illustrative to paul's answer: The tides are the (arthmetic) sum of gravitational and "centifugal" forces. If you hold a kid's hands and spin "it" (neither genders nor neutrality seems to be politically correct) around fast, you have to lean backward and your body is circling around a point between your bodies. In a stable spin this point is somewhere above your feet. But note that you are leaning backwards so that your "ponytail" is flying outwards. The very long tie that you may wearing (if given a small launch) would be pointed  outwards too, but not as strongly. If you slow down to the point where your tie knot is now closer to the kid than your feet, your tie will point towards the kid. The latter is the earthly situation. The inner tidal bulge is due to the gravitational force and the (smaller of the 2) centrifugal force(s.) and the outer bulge is sorta vice versa. Sometimes, conceptually speaking, in real world tides, it is useful to perceive the water bulges as static (wrt the moon) with the solid earth revolving within. With a frictionless, continentless earth there would be no "lag due to inertia" proposed by paul. Quibbly speaking, it's not inertia (except cornering around continents) but "friction" that provides the lag. In the real world (and hopefully one day we will have reallistically thinking humans) it's an enormously complex system and note (in the 4th diagram in the link below) that some points (mid ocean) have no tides. http://en.wikipedia.org/wiki/Tides

This was originally well laid out but the computer gods seem to be zondering me today.

paul, a quick thoughtless reply, (because the dog insists on taking me for an immediate walk) (and I have very little doubt that you are correct.)

I would have thought that through the billionia (disregarding continental drift etc) the bulge would have "caught up asymptotically" to the force(s) were there not "friction" within the water, along the coasts and as the mass(es) of water change their (vectoral) direction as they (180 degree) round the southern continental capes and the similar northern ones.

I shall be considering this on my walk and over the next few days. I would greatly appreciate a succint cerebral saving  explanation (or link) of this lag assuming a landless sphere and a sunless system. Nevertheless I will try and factor in (if relevant) "precessional" or similar considerations.

Thank you

Hay Yoo (my unforgettable chinese nickname)

Chris!, sorry

"The natural wave velocity is smaller than the Earth's rotation hence the lag."

Were the above true, surely one wouldn't have a constant lag but the lag/delay would increase steadily?

Furthermore my "friction" is not a good word when it comes to the energy "consumption" required by the mass of water turning the corner (say around S. America as the wave/bulge moves from one ocean baisin to the other. (travelling down one side, through the gap with Antarctica, and then up the other side.)

Thanks

Still thinking

hayyoo